Add dollar-quoting support to MySQL multi-query parser

[JanTvrdik]

Summary

• Add dollar-quoting ($$, $mle$, $tag$, etc.) support to the MySQL parser, reusing the same regex pattern as the PostgreSQL parser
• MySQL 9.0+ uses dollar-quoted delimiters for JavaScript stored program bodies (CREATE FUNCTION ... LANGUAGE JAVASCRIPT AS $mle$...$mle$)

Closes #34

Test plan

• Edge case tests for $mle$ and $$ delimiters with semicolons inside JS function bodies
• Nested dollar-quoted strings with different tags
• Chunk boundary test for dollar-quoted strings spanning stream chunks
• Full test suite passes (72 tests)

[Copilot]

Pull request overview

This PR extends the MySQL multi-query parser to recognize PostgreSQL-style dollar-quoted bodies (e.g. $$...$$, $mle$...$mle$) so JavaScript stored program definitions in MySQL 9.0+ can contain semicolons without prematurely terminating statements.

Changes:

• Add a dollar-quote branch to the MySQL query-splitting regex pattern.
• Add MySQL edge-case tests for $mle$ / $$ bodies, nested tags, and chunk-boundary splitting.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/MySqlMultiQueryParser.php	Adds dollar-quote matching to the MySQL statement regex.
tests/cases/MySqlMultiQueryParserTest.phpt	Adds test coverage for dollar-quoted JS stored program bodies (including chunk boundaries).

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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