Fix unsupported MySQL temporary table DDL before backend execution

[Zhengcy05]

Fixes #38709.

Changes

Changes proposed in this pull request:

• Preserve MySQL TEMPORARY semantics in CreateTableStatement and DropTableStatement
• Populate the temporary-table flag in MySQLDDLStatementVisitor
• Preserve the temporary flag during statement binding
• Add a pre-execution guard in KernelProcessor to reject CREATE TEMPORARY TABLE and DROP TEMPORARY TABLE
• Throw UnsupportedSQLOperationException before SQL is sent to backend
• Add regression tests for parser semantics, kernel guard behavior, and proxy execution flow

Tests

Added regression coverage for:

• MySQL parser / visitor temporary semantics
• kernel-level pre-execution rejection
• proxy execution flow to verify temporary table DDL does not enter metadata refresh

Executed tests:

mvn -pl parser/sql/engine/dialect/mysql -am -Dtest=MySQLStatementVisitorTest -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false test
mvn -pl infra/context -am -Dtest=KernelProcessorTest -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false test
mvn -pl proxy/backend/core -am -Dtest=StandardDatabaseProxyConnectorTest -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false test

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[Zhengcy05]

@linghengqian Sorry to bother you, the E2E test failed due to Maven download network issue, could you please help re-run the failed job?

[linghengqian]

Sorry to bother you, the E2E test failed due to Maven download network issue, could you please help re-run the failed job?

I have restarted CI.

I'm not entirely sure about the background of the original issue, and I personally think the current PR needs other committers to help review it.