Report websocket errors to stderr

[lukehutch]

Currently web socket errors are not reported to stderr in most cases (although in one strange case, they are reported and not caught by the caller: dart-lang/sdk#55664 )

This PR prints websocket errs to stderr.

Solves #1679.

Pre-launch Checklist

• I read the Contribute page and followed the process outlined there for submitting PRs.
• This update contains only one single feature or bug fix and nothing else. (If you are submitting multiple fixes, please make multiple PRs.)
• I read and followed the Dart Style Guide and formatted the code with dart format.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///), and made sure that the documentation follows the same style as other Serverpod documentation. I checked spelling and grammar.
• I added new tests to check the change I am making.
• All existing and new tests are passing.
• Any breaking changes are documented below.

[Isakdl]

LGTM