Implement the Drizzle MySQL adapter

[ian-pascoe]

Part of #54.

Goal

Complete the MySQL dialect entry point and bind approved definitions to a host-owned common Drizzle MySQL database.

Change

• Implement bindMysqlStore, DrizzleMysqlBindingError, Oracle MySQL version and engine checks, active transaction and InnoDB probes, Statement conversion, result normalization, Collection operations, candidate-key selection, stored-value readback, root mutation transactions, and structured conflict mapping.
• Preserve the exact MySQL Drizzle result type and the approved literal or runtime transaction return types.
• Compose Thread definitions through the existing generic createThreadStore seam.

Acceptance

• All 28 MySQL-focused scenarios pass.
• Base Store, SQL Statement, SQL Store, Transaction Store, combined SQL/Collection transaction, and plain plus transactional Core Runtime conformance pass.
• Scheduled Job composition and a direct Drizzle Kit export smoke test pass.
• Oracle MySQL 8.4+ is accepted; incompatible engines and unsafe key or table paths reject exactly as specified.
• The adapter uses only public Drizzle APIs, creates no client, performs no DDL, and has no MySQL runtime Store tier or Thread binder.
• Documentation, applicable changeset, focused Node.js and Bun checks, and pnpm run verify pass.

Source authority

• Drizzle MySQL Store specification
• Required cross-adapter matrix

Non-goals

No MariaDB or MySQL-compatible promise, native driver binder, host index creation, migration, preparation, streaming, batching, cancellation, or session-lock support.