[PECOBLR-1156] Add foundational structures for transaction support

Add core infrastructure for Multi-Statement Transaction (MST) support:
- Add autoCommit bool field to conn struct for client-side state caching
- Create tx struct implementing driver.Tx interface
- Add transaction error constants (Begin, Commit, Rollback, Nested, UnsupportedIsolation)
- Initialize autoCommit to true in connector (default state)

This implements the foundational structures defined in the MST design document,
following the JDBC implementation pattern with client-side autocommit caching.

Part of Epic: PECOBLR-1144 (MST Support in GoLang driver)
Design: DESIGN_MULTI_STATEMENT_TRANSACTIONS.md

Signed-off-by: Gopal Lal <[email protected]>

Author: gopalldb

connection.go

@@ -26,10 +26,16 @@ import (
 )
 
 type conn struct {
-	id      string
-	cfg     *config.Config
-	client  cli_service.TCLIService
-	session *cli_service.TOpenSessionResp
+	id         string
+	cfg        *config.Config
+	client     cli_service.TCLIService
+	session    *cli_service.TOpenSessionResp
+	autoCommit bool // Cache autocommit state client-side (default: true)
+}
+
+// tx implements driver.Tx for transaction support
+type tx struct {
+	conn *conn
 }
 
 // Prepare prepares a statement with the query bound to this connection.

connector.go

@@ -67,10 +67,11 @@ func (c *connector) Connect(ctx context.Context) (driver.Conn, error) {
 	}
 
 	conn := &conn{
-		id:      client.SprintGuid(session.SessionHandle.GetSessionId().GUID),
-		cfg:     c.cfg,
-		client:  tclient,
-		session: session,
+		id:         client.SprintGuid(session.SessionHandle.GetSessionId().GUID),
+		cfg:        c.cfg,
+		client:     tclient,
+		session:    session,
+		autoCommit: true, // Initialize autocommit cache to true (default state)
 	}
 	log := logger.WithContext(conn.id, driverctx.CorrelationIdFromContext(ctx), "")
 

errors/errors.go

@@ -17,6 +17,13 @@ const (
 	ErrParametersNotSupported            = "query parameters are not supported by this server"
 	ErrMixedNamedAndPositionalParameters = "named and positional parameters cannot be used simultaneously"
 
+	// Transaction errors
+	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"
+
 	// Request error messages (connection, authentication, network error)
 	ErrCloseConnection = "failed to close connection"
 	ErrThriftClient    = "error initializing thrift client"