[PECOBLR-1156] Add foundational structures for transaction support

[gopalldb]

Summary

Implement foundational infrastructure for Multi-Statement Transaction (MST) support in the Go driver, adding core structures and error constants needed for transaction implementation.

Changes

• Add autoCommit bool field to conn struct for client-side state caching
• Create tx struct with conn *conn field implementing driver.Tx interface
• Add 5 transaction error constants:
  • ErrTransactionBegin - "failed to begin transaction"
  • ErrTransactionCommit - "failed to commit transaction"
  • ErrTransactionRollback - "failed to rollback transaction"
  • ErrTransactionNested - "transaction already in progress"
  • ErrUnsupportedIsolation - "unsupported transaction isolation level"
• Initialize autoCommit = true in connector (default state)

Testing

• ✅ Code compiles successfully (go build ./...)
• ✅ Static analysis passes (go vet ./...)
• ✅ Pre-commit hooks passed
• Note: No functional tests in this ticket (foundational structures only)
• Full testing will be implemented in PECOBLR-1160 and PECOBLR-1161

JIRA

Closes PECOBLR-1156 Part of Story: PECOBLR-1155 Part of Epic: PECOBLR-1144

Design Document

See DESIGN_MULTI_STATEMENT_TRANSACTIONS.md for complete technical design. This implementation follows Section 3.1 (tx struct), Section 4.1 (autoCommit field), Section 4.2 (initialization), and Section 5.1 (error constants).

Implementation Notes

• Follows JDBC implementation pattern (PR #1060) with client-side autocommit caching
• No user-facing changes in this ticket (structures only)
• Ready for PECOBLR-1157 (BeginTx implementation)

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]