Add ESM support and dual-mode imports to Node.js bindings

[YannDanthu]

Summary

This PR adds dual CommonJS/ESM support to the Node.js bindings, allowing the package to be used with both require() and import statements.

Changes

• ✅ Add ESM build output (gtfs-realtime.mjs, types.d.mts)
• ✅ Update package.json with conditional exports for dual-mode support
• ✅ Split buildProto script into modular cjs/esm build targets
• ✅ Automate Long import fix to use protobufjs stub type
• ✅ Automate default export syntax fix for ESM
• ✅ Remove 'type: commonjs' field to allow proper dual-mode resolution
• ✅ Document git submodule initialization requirement

Usage

The package now automatically serves the correct module format based on the importing environment:

ESM:

import { transit_realtime } from 'gtfs-realtime-bindings-transit';

CommonJS:

const GtfsRealtimeBindings = require('gtfs-realtime-bindings-transit');

Backward Compatibility

Full backward compatibility maintained with existing CommonJS users.

Test Plan

• Test ESM imports in a module project
• Test CommonJS requires in a traditional Node.js project
• Verify TypeScript type definitions work for both formats

[magoni]

Looks fine to me, although I haven't tested the changes.

Do we need to manually increment the version?

Since I'm less familiar with this project I'll let another maintainer weigh in for the final review

[YannDanthu]

Looks fine to me, although I haven't tested the changes.

Do we need to manually increment the version?

Since I'm less familiar with this project I'll let another maintainer weigh in for the final review

good point.
the nodes/UPDATING.md says yes.
and I guess after the PR merge we have to do a npm publish

[cmonagle]

Didn't test, but LGTM.