Update dependency protobuf to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
protobuf (source)	dependencies	major	^2.0.0 → ^6.0.0

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Release Notes

google/protobuf.dart (protobuf)

v6.0.0

Compare Source

• New GeneratedMessage extension methods toTextFormat and writeTextFormat
  added to convert the message into the official protocol buffers text
  format. (#​1080, #​125)

• Add well-known proto types as libraries. This change is required for
  protoc_plugin-25.0.0. (#​1081)

• Breaking: Hide PbList and PbMap constructors. It is not possible to
  construct these values correctly in user code, so the constructors are now
  private. Existing uses of PbList can be replaced by List and PbMap can
  be replaced by Map.

  For immutable lists and maps, you can use built_value. (#​1072)

• Map fields now check key and value validity when adding elements. (#​1065,
  #​1076)

v5.1.0

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• Update default size limit of CodedBufferReader from 67,108,864 bytes to
  2,147,483,647 bytes, and default recursion limit from 64 to 100.

  The new limits are consistent with the Java and C++ implementations. (#​1060)

• Fix GeneratedMessage.addExtension returning non-frozen and
  GeneratedMessage.getExtension allowing modifying an extension when the
  message is frozen before initializing the extension field set. (#​1062)

• Fix GeneratedMessage.getExtension returning differently typed lists when the
  message extension field set is initialized and frozen and initialized but not
  frozen. (#​1062)

• Fix PbList methods addAll, insertAll, replaceRange, setAll,
  setRange iterating the Iterable argument twice. (#​730, #​1070)

• Fix GeneratedMessage.== throwing a type error when comparing map fields in
  some cases. (#​1075, #​1077)

  This bug was introduced with protobuf-5.0.0.

v5.0.0

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• Improve performance of GeneratedMessage.deepCopy. (#​742)
• Fix unknown enum handling in GeneratedMessage.mergeFromProto3Json when
  the ignoreUnknownFields optional argument is true. (#​853)
• Add BuilderInfo methods to support protoc-plugin 23.0.0. (#​1047)
• Generalize argument type of PbList.from from List<T> to Iterable<T>.
  (#​1054)
• Fix clearing oneof fields with GeneratedMessage.clear. (#​1057)
• Fix unknown JSON handling when using GeneratedMessage methods
  mergeFromJson, mergeFromJsonMap, writeToJson, writeToJsonMap.
  (#​1058)

v4.2.0

Compare Source

• Internal refactoring to split the package into libraries. This allows
  conditionally importing different libraries and improving performance by
  using different encoding/decoding libraries based on the target platform.
  (#​1026)

• Some of the private PbFieldType members are made public, to allow using
  them in internal libraries. This type is for internal use only. (#​1027)

• Improve performance of GeneratedMessage members: writeToJsonMap,
  writeToJson, mergeFromJson, mergeFromJsonMap. (#​1028)

• Remove BuilderInfo.fromProto3Json and BuilderInfo.toProto3Json as a part
  of an internal refactoring.

v4.1.1

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• Minimum SDK dependency bumped from 3.6.0 to 3.7.0. (#​1024)

v4.1.0

Compare Source

• Improve packed field decoding performance. (#​959, #​981)
• Minimum SDK dependency bumped from 3.3.0 to 3.6.0. (#​1001)

v4.0.0

Compare Source

• Breaking: The following types and members are now removed:

  • PbEventMixin
  • PbFieldChange
  • EventBuffer
  • GeneratedMessage.createRepeatedField
  • GeneratedMessage.createMapField

  These were used to implement events, which are unused internally. To keep API
  surface small (to make it easier to change the library or migrate to another
  library) these types and members are removed. (#​738)

• Breaking: CodedBufferWriter.writeRawBytes now takes a Uint8List
  argument (instead of TypedData).

• GeneratedMessageGenericExtensions.deepCopy is now annotated with
  @useResult and will generate a warning when its result is not used.
  (#​896)

• Breaking: PbMap.unmodifiable now takes key and value field types as
  arguments, instead of another PbMap.

  To migrate, use PbMap.unmodifiable(map.keyFieldType, map.valueFieldType)
  instead of PbMap.unmodifiable(map). (#​902)

• Messages deserialized from JSON now generate the unknown fields when
  serialized as JSON.

  Note that, as before, unknown fields in JSON messages are not stored in the
  unknownFields of the message. They are only used by the JSON serializers to
  support roundtripping.

  (#​49, #​918)

• Minimum SDK dependency bumped from 2.19.0 to 3.3.0. (#​953)

v3.1.0

Compare Source

• CodedBufferReader readBytes now copies the returned bytes to avoid
  accidental sharing of the input buffer with the returned Uint8List. New
  member readBytesAsView added with the old behavior. (#​863)

• Avoid sharing the input buffer in unknown length-delimited fields using the
  new readBytes. (#​863)

v3.0.0

Compare Source

• Require Dart 2.19.
• Remove ReadonlyMessageMixin (#​183, #​644)
• Remove frozenMessageModificationHandler (#​175, #​643)
• Remove PbListBase and FrozenPbList types. All proto repeated fields now
  use PbList. To check if a list is frozen, use isFrozen getter. (#​624,
  #​626)
• Initialize map fields in GeneratedMessage.getField. This behavior is
  consistent with getField called on repeated fields. (#​373, #​707)
• Remove unused and optional PbMap constructor argument BuilderInfo? info.
  (d94d3f0)
• UnknownFieldSetField methods hasRequiredFields, isInitialized and
  getter length removed. (#​721)
• Update library documentation to hide internals, add documentation for public
  types. (#​681)
• Fix PbMap._isReadonly field initialization in PbMap.unmodifiable.
  (#​741, #​754)
• Fix decoding map fields when key or value (or both) fields of a map entry is
  missing. (#​719, #​745)
• Fix updating frozen (immutable) messages with merge methods
  (mergeFromBuffer, mergeFromProto3Json, ...). (#​489, #​727)
• Fix handling null values in proto3 JSON deserializer. (#​751, #​760,
  #​763)
• Fix handling negative JSON values when parsing uint32 fields. (#​839)
• Avoid serializing unknown fields twice in reparseMessage. (#​840)

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The artifact failure details are included below:

File name: pubspec.lock

Command failed: flutter pub upgrade protobuf
Because every version of flutter_test from sdk depends on meta 1.3.0-nullsafety.3 and nakama_flutter depends on meta ^1.3.0, flutter_test from sdk is forbidden.
So, because nakama_flutter depends on flutter_test any from sdk, version solving failed.
pub upgrade failed (1; So, because nakama_flutter depends on flutter_test any from sdk, version solving failed.)