fix(connect/ws): ensure proxy stream is writable

[jzaefferer]

Here the proxy stream is being written, so we need to check if it is writable ("which means the stream has not been destroyed, errored, or ended, see https://nodejs.org/dist/v18.19.0/docs/api/stream.html#writablewritable ).

Fixes #1914

I could reproduce the 'stream.push() after EOF' error in an app, but unfortunately have no idea how to use it for a reproduction. Hopefully this patch provides enough inspiration to write a test.

[robertsLando]

Thanks @jzaefferer nice catch!

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.34%. Comparing base (a6e74ad) to head (7a8d81e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/connect/ws.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2024   +/-   ##
=======================================
  Coverage   83.34%   83.34%           
=======================================
  Files          25       25           
  Lines        1585     1585           
  Branches      367      367           
=======================================
  Hits         1321     1321           
  Misses        230      230           
  Partials       34       34           

Flag	Coverage Δ
unittests	83.34% <0.00%> (ø)

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