fix(mysql): type binary/varbinary as Buffer instead of string

[manja316]

Summary

MySQL binary and varbinary columns store raw byte data. The mysql2 driver correctly parses these as Buffer, but drizzle-orm was converting them to strings via .toString(), losing binary semantics.

• Changes dataType from 'string' to 'buffer' for MySqlBinary and MySqlVarBinary
• Changes data and driverParam types from string to Buffer
• Updates mapFromDriverValue to return Buffer directly instead of converting to string
• Follows the same pattern as SQLiteBlobBuffer which correctly uses dataType: 'buffer'

Breaking Change

This is a type-level breaking change. Users who relied on binary()/varbinary() returning string will need to update their code:

// Before
const row = await db.select().from(table);
row.binaryCol; // string

// After
const row = await db.select().from(table);
row.binaryCol; // Buffer
row.binaryCol.toString(); // string (if needed)

Test Plan

• Type tests pass (pnpm test:types in drizzle-orm)
• Updated type test defaults from '' to Buffer.from('')
• Integration tests (require MySQL instance)

Note

The same issue exists in singlestore-core columns — left as a follow-up to keep this PR focused.

Fixes #1188

/claim #1188