Allow custom types to wrap selected column SQL

[partyplatter08-lab]

/claim #554

Summary

• add selectFromDb(column) to customType params so custom columns can wrap their selected column SQL before driver decoding
• apply the wrapper in select/returning SQL generation for PostgreSQL, MySQL, SQLite, SingleStore, and Gel custom columns, including relational JSON selection paths
• document the new option and add SQL generation coverage for PostgreSQL, MySQL, and SQLite

Assumption

• The public API name is selectFromDb, and it receives already-qualified column SQL where the dialect would normally emit the selected column.

Tests

• corepack pnpm --dir drizzle-orm test -- custom-type-select.test.ts
• corepack pnpm --dir drizzle-orm test:types
• corepack pnpm lint
• git diff --check
• PATH="$PWD/.tmp-bin:$PATH" corepack pnpm --dir drizzle-orm build