feat(go): support transactions and isolation level

[VishalGG]

What's Changed

Implement transaction support (autocommit toggle, Commit, Rollback) and
isolation-level support for the MySQL ADBC driver.

• mysqlConnectionImpl now implements driverbase.AutocommitSetter
  (auto-registered by sqlwrapper via type assertion): SetAutocommit(false)
  issues BEGIN; SetAutocommit(true) issues COMMIT. The driverbase
  wrapper still short-circuits Commit/Rollback to StatusInvalidState
  when autocommit is enabled.
• Commit/Rollback use chained-transaction semantics (COMMIT then
  BEGIN) so the next statement continues to run inside a transaction
  until the caller re-enables autocommit — matches the Snowflake driver's
  pattern (snowflake/go/connection.go:800-826).
• OptionKeyIsolationLevel is translated to
  SET SESSION TRANSACTION ISOLATION LEVEL ... and applied immediately.
  LevelDefault maps to REPEATABLE READ (MySQL's documented default
  and the same convention the C++ PostgreSQL driver uses at
  arrow-adbc/c/driver/postgresql/connection.cc:1215). LevelSnapshot
  and LevelLinearizable are not supported and return
  StatusNotImplemented per ADBC spec.
• GetOption(OptionKeyIsolationLevel) returns the cached level.
• SupportsTransactions capability flag flipped to true in both Go
  quirks (mysql_test.go) and Python validation
  (validation/tests/mysql.py).
• Removed obsolete pytest.ini filter that suppressed
  "Cannot disable autocommit; conn will not be DB-API 2.0 compliant"
  warnings — no longer triggered now that autocommit toggling works.
• Added integration tests covering transaction commit/rollback durability
  and isolation-level round-trips against a live MySQL server.

Closes #55.
Closes #34.

[Mandukhai-Alimaa]

Since this driver uses the shared sqlwrapper, would it make sense to implement transactions there using Go’s database/sql transaction API instead of managing them with raw BEGIN/COMMIT statements here?

[VishalGG]

Since this driver uses the shared sqlwrapper, would it make sense to implement transactions there using Go’s database/sql transaction API instead of managing them with raw BEGIN/COMMIT statements here?

yes, this makes sense. I saw there is already an existing issue adbc-drivers/driverbase-go#28 . Will look into that and see if i can implement transactions there and raise a PR.