feat(cloudflare): add custom domain support for R2 buckets

[agcty]

Adds comprehensive custom domain configuration for Cloudflare R2 buckets with automatic DNS management, enabling production-ready content
delivery through custom domains.

Features

• Custom Domain Configuration: New customDomain property on R2Bucket supporting:

  • Domain name and Cloudflare Zone ID
  • TLS version control (1.0, 1.1, 1.2, 1.3)
  • Custom cipher suite configuration
  • Enable/disable toggle

• Automatic DNS Management:

  • Automatically creates proxied CNAME records pointing to public.r2.dev
  • Handles DNS record lifecycle (create, update, delete)
  • Detects and preserves read-only records created by Cloudflare dashboard
  • Cleans up DNS records when custom domain is removed

• Full CRUD Support:

  • Create custom domains with automatic DNS setup
  • Update domain settings (TLS, ciphers, enabled state)
  • Handle domain name changes (deletes old, creates new)
  • Clean deletion of both custom domain and DNS records

Example Usage

import { R2Bucket } from "alchemy/cloudflare";

const cdnBucket = await R2Bucket("cdn-assets", {
  name: "cdn-assets",
  customDomain: {
    domain: "cdn.example.com",
    zone: "zone or zone-id",
    enabled: true,
    minTLS: "1.2"
  }
});

// DNS record is automatically created
console.log(cdnBucket.customDomain?.domain); // "cdn.example.com"

Test Coverage

- ✅ Create custom domain with automatic DNS record
- ✅ Verify DNS record configuration (CNAME, proxied)
- ✅ Update custom domain settings (TLS, enabled state)
- ✅ Remove custom domain with DNS cleanup
- ✅ Handle read-only DNS records from dashboard

Documentation

- Added "With Custom Domain" section to R2 Bucket docs
- Includes examples and feature highlights

API References

- https://developers.cloudflare.com/api/resources/r2/subresources/custom_domains/
- https://developers.cloudflare.com/api/resources/dns/subresources/records/

Implements #1107 

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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