Add dual module support (ESM + CommonJS)

[jariy17]

Summary

Add support for both ESM and CommonJS module systems to improve compatibility with projects using CommonJS resolution (e.g., tsx with CommonJS projects).

Background

Currently, this package is ESM-only ("type": "module"). Users with CommonJS projects encounter module resolution errors when trying to import this package.

Related: #42, PR #43

Proposed Solution

Implement dual module support following the AWS SDK pattern:

1. Separate build outputs: dist-cjs/ (CommonJS) and dist-es/ (ESM)
2. Update package.json exports:

   "exports": {
     ".": {
       "require": "./dist-cjs/index.js",
       "import": "./dist-es/index.js",
       "types": "./dist-types/index.d.ts"
     }
   }

3. Add separate TypeScript configs for each module format

Alternatives Considered

• Bundler approach (tsup/esbuild): Single config generates both formats
• Keep ESM-only: Document requirement for users to configure their projects for ESM

Current Workaround

Users can add "type": "module" to their project's package.json to enable ESM resolution.