feat: Add multi-statement transaction support (#704)

Implement PEP 249-compliant transaction control with extensions for
manual commit/rollback operations. This enables atomic multi-table
operations with REPEATABLE_READ isolation semantics.

Core API additions:
- connection.autocommit property for enabling/disabling auto-commit mode
- connection.commit() to commit active transactions
- connection.rollback() to rollback active transactions
- connection.get_transaction_isolation() returns current isolation level
- connection.set_transaction_isolation() validates isolation level
- TransactionError exception for transaction-specific failures

Implementation details:
- Added autocommit state caching in Session with optional server query
- Added TRANSACTION_ISOLATION_LEVEL_REPEATABLE_READ constant
- All transaction operations include proper error handling and telemetry
- Supports fetch_autocommit_from_server connection parameter

Testing:
- Unit tests covering all transaction methods and error scenarios
- e2e integration tests validating transaction behavior including
  multi-table atomicity, sequential transactions, and isolation semantics

Documentation:
- Comprehensive TRANSACTIONS.md guide with examples and best practices
- Updated README.md with basic usage and reference to detailed docs

Requires MST-enabled Databricks SQL warehouse and Delta tables with
'delta.feature.catalogOwned-preview' table property.

---------

Signed-off-by: Jayant Singh <[email protected]>

Author: jayantsing-db

README.md

@@ -67,6 +67,12 @@ or to a Databricks Runtime interactive cluster (e.g. /sql/protocolv1/o/123456789
 > to authenticate the target Databricks user account and needs to open the browser for authentication. So it 
 > can only run on the user's machine.
 
+## Transaction Support
+
+The connector supports multi-statement transactions with manual commit/rollback control. Set `connection.autocommit = False` to disable autocommit mode, then use `connection.commit()` and `connection.rollback()` to control transactions.
+
+For detailed documentation, examples, and best practices, see **[TRANSACTIONS.md](TRANSACTIONS.md)**.
+
 ## SQLAlchemy
 Starting from `databricks-sql-connector` version 4.0.0 SQLAlchemy support has been extracted to a new library `databricks-sqlalchemy`.