arrow-ipc: Ensure writer conforms to spec on length-0 variable-size arrays

[atwam]

Which issue does this PR close?

• Closes arrow-ipc writer does not comply with spec for empty variable-size arrays #9716 .

Rationale for this change

Current version serializes a length-0 offsets buffer, and relies on the array constructor to set offsets to [0] for empty arrays. This does not conform with spec, which specifies that the offsets buffer should have length + 1 elements.

This correctly serializes a length-1 offsets buffer containing [0]. I have left the current behavior of filling-in offsets with [0] for empty arrays, so that future versions can still read IPC files serialized by previous versions.

What changes are included in this PR?

Added tests for serialization of empty arrays, ensuring length-1 offsets buffer. Fixed serialization of empty arrays.
This fixes serialization of empty Binary/Utf8/List/LargeList (and Map) arrays.

Are these changes tested?

Yes

Are there any user-facing changes?

There should not be any breaking change for users. Serialized files for empty record batches will be slightly different. Older serialized files should still be read fine.

[alamb]

Current version serializes a length-0 offsets buffer, and relies on the array constructor to set offsets to [0] for empty arrays. This does not conform with spec, which specifies that the offsets buffer should have length + 1 elements.

I don't understand this statement. The spec you reference in #9716 is for the in memory structure (not the ipc format)

It almost sounds like a bug in polars -- shouldn't it accept zero length IPC buffers ?