test: test closing handshake, fix autobahn output dir

[mccutchen]

What it says on the tin, a couple of fixups extracted from #23

[github-actions]

🔥 Run benchmarks comparing 482eb71 against main:

gh workflow run bench.yaml -f pr_number=29

Note: this comment will update with each new commit.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.62%. Comparing base (784b11d) to head (482eb71).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
websocket.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #29   +/-   ##
=======================================
  Coverage   79.62%   79.62%           
=======================================
  Files           3        3           
  Lines         432      432           
=======================================
  Hits          344      344           
  Misses         64       64           
  Partials       24       24           

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