websockets: fix ping_timeout (#3376)

websockets: fix ping_timeout (#3376)

* websockets: fix ping_timeout

* Closes #3258
* Closes #2905
* Closes #2655
* Fixes an issue with the calculation of ping timeout interval that
  could cause connections to be erroneously timed out and closed
  from the server end.

* websocket: Fix lint, remove hard-coded 30s default timeout

* websocket_test: Improve assertion error messages

* websocket_test: Allow a little slack in ping timing

Appears to be necessary on windows.

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Co-authored-by: Ben Darnell <ben@bendarnell.com>