fix(handler): optimise snapshot hanlding (#8652)

# Which Problems Are Solved

There are cases where not all statements of multiExec are succeed. This
leads to inconsistent states. One example is [LDAP
IDPs](https://github.com/zitadel/zitadel/issues/7959).

If statements get executed only partially this can lead to inconsistent
states or even break projections for objects which might not were
correctly created in a sub table.

This behaviour is possible because we use
[`SAVEPOINTS`](https://www.postgresql.org/docs/current/sql-savepoint.html)
during each statement of a multiExec.

# How the Problems Are Solved

SAVEPOINTS are only created at the beginning of an exec function not
during every execution like before. Additionally `RELEASE` or `ROLLBACK`
of `SAVEPOINTS` are only used when needed.

# Additional Changes

- refactor some unused parameters

# Additional Context

- closes https://github.com/zitadel/zitadel/issues/7959

internal/eventstore/handler/v2/statement.go

@@ -677,18 +677,6 @@ func exec(config execConfig, q query, opts []execOption) Exec {
 			opt(&config)
 		}
 
-		_, err = ex.Exec("SAVEPOINT stmt_exec")
-		if err != nil {
-			return zerrors.ThrowInternal(err, "CRDB-YdOXD", "create savepoint failed")
-		}
-		defer func() {
-			if err != nil {
-				_, rollbackErr := ex.Exec("ROLLBACK TO SAVEPOINT stmt_exec")
-				logging.OnError(rollbackErr).Debug("rollback failed")
-				return
-			}
-			_, err = ex.Exec("RELEASE SAVEPOINT stmt_exec")
-		}()
 		_, err = ex.Exec(q(config), config.args...)
 		if err != nil {
 			return zerrors.ThrowInternal(err, "CRDB-pKtsr", "exec failed")