Support ESM package export

[re-taro]

Summary

Add ESM (ECMAScript Module) support alongside existing CommonJS compatibility. This change enables the package to be used with both import and require statements, providing better compatibility with modern JavaScript tooling and environments.

Resolves: #346
Resolves: #347

Changes

• Package Configuration: Added dual package exports with proper conditional exports for ESM and CommonJS
• Build System: Implemented custom build script to generate both ESM and CommonJS outputs
• TypeScript Configuration: Split build configuration into separate files for ESM and CommonJS compilation targets
• Module Type: Set package type to "module" as the primary format while maintaining CommonJS compatibility

Technical Details

• ESM output is placed in dist/ directory as the default export
• CommonJS output is placed in dist/cjs/ directory with its own package.json specifying "type": "commonjs"
• Build script handles proper package.json generation for distribution
• Size limits updated to monitor both ESM and CommonJS bundle sizes

Breaking Changes

None. This change maintains full backward compatibility with existing CommonJS consumers while adding ESM support.

[re-taro]

@blakeembrey @bjohansebas

Please let me know your thoughts at your earliest convenience.

[UlisesGascon]

@re-taro there is a policy in the oven regarding ESM expressjs/discussions#323. I hope that this can give you additional context 👍

[blakeembrey]

Unfortunately, as mentioned in the issues you linked to, this won't land until there's a new major. I don't believe this is backward compatible because anyone it will change the imports for anyone using ESM to import from CommonJS today.