feat: Add Bun runtime compatibility layer

[lalalune]

Summary

This adds a Bun-compatible API layer for workerd, enabling Bun applications to run on Cloudflare Workers infrastructure.

Usage

pnpm run build:bun

// worker.js
import Bun from './bun-bundle.js'

export default {
  async fetch(request) {
    const hash = Bun.hash('hello world')
    await Bun.write('/tmp/data.txt', 'Hello from Bun')
    const file = Bun.file('/tmp/data.txt')
    const content = await file.text()
    
    return new Response(JSON.stringify({
      hash: hash.toString(16),
      content,
      bunVersion: Bun.version
    }))
  }
}

Features

• File Operations: Uses node:fs (same filesystem limitations as nodejs_compat; typically /tmp with enable_web_file_system)
• Password Hashing: PBKDF2 via WebCrypto
• DNS: Real DNS-over-HTTPS (DoH) via Cloudflare/Google
• SQLite: In-memory SQLite implementation
• Hashing: wyhash, crc32, adler32, cityhash32/64, murmur32v3/64v2
• Utilities: sleep, escapeHTML, stringWidth, deepEquals, inspect, streams

Samples

• samples/bun-bundle/ - Demonstrates bundled compatibility layer
• samples/bun-hello/ - Demonstrates native bun:* imports

Files Changed

• src/bun/ - TypeScript implementation (14 files)
• src/workerd/api/bun/ - C++ integration (2 files)
• src/workerd/api/modules.h - Module registration
• src/workerd/api/BUILD.bazel - Build dependencies
• samples/bun-bundle/ and samples/bun-hello/ - Sample workers

Test Results

• bun.test.ts: 180 tests passed
• sqlite.test.ts: 26 tests passed
• dns.test.ts: 15 tests passed

[github-actions]

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[jasnell]

While we appreciate outside contributions, at this time we do not intend to impl (or add someone else's impl) of any bun-specific APIs to the Workers runtime. It is something we've discussed and have currently ruled out. There is just simply not enough ecosystem demand to justify the effort that would be needed to maintain it. It's conceivable that at some future point in time we might reconsider but it's unlikely to be any time soon.

(I left this comment in the original PR as well)

[lalalune]

okay makes sense, will close