feat: add ESM entrypoint and TypeScript exports

[luzzwaix]

@algora-pbc /claim #135

Closes #135.

Adds package-level ESM and TypeScript support while preserving CommonJS compatibility.

Verification:

• npx tap --disable-coverage test/esm.js test/typescript.js
• npm run lint
• git diff --check
• npm pack --dry-run

[esatterwhite]

I'll refer you to this comment
#144 (comment)

What problem are we actually trying to solve here?

[luzzwaix]

I'll refer you to this comment #144 (comment)

What problem are we actually trying to solve here?

@algora-pbc /claim #135

Thanks, that makes sense. I narrowed the PR around the problem you described in the earlier comment.

The goal here is not to migrate the project to TypeScript or make ESM the primary runtime format. CommonJS remains the implementation and there is still no build step.

This now focuses on:

• package exports so both require("seeli") and import seeli from "seeli" resolve through the same CommonJS entrypoint
• TypeScript declarations for CommonJS and NodeNext/ESM consumers
• a default alias on the CommonJS export for interop
• tests proving CommonJS compatibility, default ESM import, and TypeScript NodeNext usage

I removed the separate ESM shim and kept the runtime surface closer to the existing package design.