feat: release for all compatible envs

[mandarini]

This PR ensures iceberg-js works in all JavaScript/TypeScript environments.

Changes

Package exports:

• ESM support with .mjs files and proper exports field
• CommonJS support with .cjs files
• Separate type definitions for ESM (.d.ts) and CJS (.d.cts)
• Fixed tsup config to generate correct file extensions

Compatibility testing:

• Added comprehensive tests for 4 scenarios: pure JS ESM, pure JS CJS, TypeScript ESM, TypeScript CJS
• Tests run on Node.js 20 & 22 in CI

CI improvements:

• Reorganized workflows: main ci.yml orchestrates parallel execution of test.yml, integration-test.yml, and new compatibility.yml
• All sub-workflows support manual triggering via workflow_dispatch

Documentation:

• Added compatibility matrix to README
• Added development docs for running compatibility tests

The package now works seamlessly with both import and require(), in all bundlers, and with full TypeScript support in any module configuration.

[pkg-pr-new]

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npm i https://pkg.pr.new/supabase/iceberg-js@15

commit: 0f49950