Add bussql transaction utilities and context propagation

[molon]

No description provided.

[Copilot]

Pull request overview

This PR introduces a shared bussql package for transaction management and context-based executor propagation, and refactors the bus and PostgreSQL dialect to use it. It also wires in SQLite for transaction tests and slightly tightens the repo’s ignore patterns.

Changes:

• Add bussql package with Executor, FromContext/NewContext, and Transaction/savepoint logic plus comprehensive unit tests (using SQLite).
• Replace the BeginTx-style transaction handling in bus.BusImpl.Publish and pgbus.Dialect (Upsert, delete, drain) with a new ExecTx method that leverages bussql.
• Update module dependencies and .gitignore to support the new tests and ignore test binaries.

Reviewed changes

Copilot reviewed 8 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
.gitignore	Adds patterns to ignore __debug* and *.test binaries, keeping the repo clean from local build artifacts.
go.mod	Adds a dependency on github.com/mattn/go-sqlite3 for running the new database-backed tests.
go.sum	Records checksums for the added SQLite dependency to keep module verification consistent.
bus.go	Refactors BusImpl.Publish to run job enqueuing inside Dialect.ExecTx, enabling reuse of ambient transactions via bussql and simplifying local transaction management.
dialect.go (root)	Updates the Dialect interface to expose ExecTx (and removes BeginTx), codifying transaction orchestration at the dialect level.
pgbus/dialect.go	Implements ExecTx using bussql.Transaction + FromContext/NewContext, and refactors Upsert, delete, and drain to use this shared transaction wrapper.
bussql/context.go	Introduces the Executor abstraction plus FromContext/NewContext helpers to propagate DB/Tx instances via context.Context.
bussql/context_test.go	Verifies FromContext/NewContext behavior, including overriding executors, nil handling, and fallback semantics.
bussql/tx.go	Provides generic Transaction and nested-savepoint logic with robust rollback/commit behavior and context-cancellation handling.
bussql/tx_test.go	Adds extensive tests (backed by in-memory SQLite) covering basic, rollback, nested, savepoint, and context-cancellation scenarios for Transaction.

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