[Mysql] Fix binary/varbinary column types as Buffer

[ThaiTrevor]

🤖 AI-assisted contribution — This PR was drafted with AI assistance and reviewed by a native Vietnamese speaker before submission. Placeholders, terminology, and file format were validated automatically. I will respond to review feedback. Happy to revise or close if not a fit.

---

Summary

Closes #1188.

mysql2 returns BINARY / VARBINARY columns as a Node Buffer, but drizzle-orm typed the column data as string and lossily called Buffer.prototype.toString() on the driver value in mapFromDriverValue. That silently corrupted any non-UTF-8 binary content (e.g. a UUID stored as binary(16), or a hash stored as varbinary(32)).

This aligns the column data type with what the driver actually returns:

• dataType is now 'buffer' (same convention as sqlite-core blob in buffer mode).
• The inferred data type is Buffer; driverParam accepts Buffer | string since mysql2 also accepts hex strings as input.
• mapFromDriverValue returns the Buffer as-is (or wraps a Uint8Array / string via Buffer.from) instead of stringifying it.

Files changed

• drizzle-orm/src/mysql-core/columns/binary.ts
• drizzle-orm/src/mysql-core/columns/varbinary.ts
• drizzle-orm/type-tests/mysql/tables.ts — update .default('') to .default(Buffer.from('')) so the existing type test continues to compile against the new type.
• integration-tests/tests/mysql/mysql-common.ts — update the mysql "all types" suite to insert/expect Buffer for the binary and varbin columns.

Note for maintainers

This is a typed-API change for users who relied on the previous string inference, but the previous runtime behaviour was already broken for true binary payloads (silent UTF-8 conversion), so this aligns the types with the driver's real output and lets users store/retrieve binary data safely.

The parallel files in singlestore-core (columns/binary.ts, columns/varbinary.ts) share the same broken pattern; they are intentionally left untouched here to keep this PR scoped to the issue, but happy to apply the same fix in a follow-up if you'd like.

Test plan

• pnpm --filter drizzle-orm test:types — type-tests in drizzle-orm/type-tests/mysql/tables.ts now assert Buffer instead of string for binary / varbinary.
• cd integration-tests && pnpm test — mysql "all types" test inserts a Buffer and asserts it is returned as Buffer.

[ThaiTrevor]

Quick check-in — anything I can adjust to make this easier to review? Happy to break it down, add tests, or revise the approach. Thanks!