feat(drivers): add Bun-native Redis, SQLite, and Postgres adapters

[unisol1020]

Adds first-class support for Bun runtime users by introducing three new driver entry points that talk to Bun's built-in clients directly, bypassing the Node-targeted bindings used by the existing drivers. Existing drivers stay untouched — Bun is an opt-in alternative, not a replacement.

New drivers (all L2, Bun runtime only):

• bentocache/drivers/bun_redis → bunRedisDriver, uses import { RedisClient } from 'bun'. No ioredis dependency. Implements get/set (PX TTL)/pull (GETDEL)/delete/deleteMany (UNLINK)/ clear (SCAN + UNLINK loop)/namespace/disconnect.

• bentocache/drivers/bun_sqlite → bunSqliteDriver, plugs a new BunSqliteAdapter into the existing DatabaseDriver. Uses bun:sqlite Database + prepared statements (lazily built so they reference the table only after setTableName). deleteMany runs inside a single transaction.

• bentocache/drivers/bun_postgres → bunPostgresDriver, plugs BunPostgresAdapter into DatabaseDriver. Built on import { SQL } from 'bun' tagged-template queries with identifier interpolation via sql(tableName). Same column shape as the existing Kysely PG path (key PK, value TEXT, expires_at BIGINT). Postgres has no native TTL so users should set pruneInterval — same caveat as the existing pg adapters.

Runtime compatibility:

• No engines restriction; Node users see no behaviour change.
• All Bun imports in the type layer use import type only, so drivers_options.ts still loads cleanly under Node.
• require('bun') / require('bun:sqlite') live only inside the new driver files. A Node user accidentally importing them gets a clear ERR_MODULE_NOT_FOUND.

Tests:

• Three new spec files under tests/drivers/bun_*.spec.ts that gate registration on typeof Bun !== 'undefined' and dynamically import the driver inside the guard, so Japa loads them on Node without resolving Bun-only modules. Reuse registerCacheDriverTestSuite for the standard get/set/pull/delete/deleteMany/clear/namespace/TTL coverage.
• New quick:test:bun script (bun bin/test.ts) for running the Bun specs locally.
• Verified end-to-end: Node typecheck/lint/build clean; Node tests run unchanged (existing memory/redis suites pass, Bun specs report NO TESTS EXECUTED); under Bun, all three specs pass (22 + 21 + 21).

Docs:

• quick_setup.md and telemetry.md codegroups gain a bun tab next to npm/pnpm/yarn.
• packages/otel/README.md install block now lists all four package managers.
• cache_drivers.md gets three new sections (Bun Redis, Bun SQLite, Bun Postgres). Each is explicitly tagged "L2 driver, Bun runtime only" so the topology constraint is discoverable in-page.

Package wiring:

• Three new ./drivers/bun_* entries in package.json exports map.
• @types/bun added to devDependencies (no peerDep — Bun is a runtime, not an npm package consumers install).

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