fix: memoize RTCDataChannel fields

[achingbrain]

Stores local copies of the id, label and protocol fields for RTCDataChannel polyfill objects.

This is because libdatachannel throws if these fields are accessed on a DataChannel after it's been closed, but browsers allow access so brings the polyfill in line with other implementations.

[ThaUnknown]

it's one of the things i fixed in ##324 ;-;

[mertushka]

@murat-dogan Can you merge this please?

[murat-dogan]

Hello @achingbrain ,

I am not sure about the tests.
I mean we can not write all tests for polyfills, and actually, we don't need it.
We want to pass WPT tests as much as we can.

I think just a basic polyfill test will be enough.

[mertushka]

@achingbrain @murat-dogan After applying the readyState fix #359 and run the build workflows, this test "it can access datachannel informational fields after closing" is failing with a timeout, but only on macOS (x64). Interestingly, the same test passes without issues on the Linux builds. It's a bit puzzling.

You can see the Build - Mac x64 failure here:
https://github.com/mertushka/node-datachannel/actions/runs/15748038280/job/44388296991#step:6:26

[mertushka]

After re-running the workflow without any changes, the test passed on macOS (x64). I guess it was something on the GitHub Runner's side? Pretty weird.

https://github.com/mertushka/node-datachannel/actions/workflows/build-mac-x64.yml