refactor: {Read,Write}Message return errors without closing connection

[mccutchen]

The idea here is:

• Use the Serve() method for a high-level API that will automatically close the connection when errors are encountered
• Use the ReadMessage()/WriteMessage()/CloseWithStatus() methods to have more control over connection lifecycle, including the decision about when a read or write error should close the connection

I think this improves the API by making it more explicit, and also simplifies some tests.

[github-actions]

🔥 Run benchmarks comparing c135432 against main:

gh workflow run bench.yaml -f pr_number=68

Note: this comment will update with each new commit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.11%. Comparing base (8744466) to head (c135432).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #68      +/-   ##
==========================================
+ Coverage   96.99%   98.11%   +1.12%     
==========================================
  Files           2        2              
  Lines         432      425       -7     
==========================================
- Hits          419      417       -2     
+ Misses          7        4       -3     
+ Partials        6        4       -2     

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