fix: propagate dispatcher options to base class

[mcollina]

Pass dispatcher options to DispatcherBase in proxy and pool wrappers so their configured WebSocket limits are exposed to the WebSocket parser instead of being replaced by the defaults.

Add regression coverage for BalancedPool, RoundRobinPool, ProxyAgent, EnvHttpProxyAgent, and Socks5ProxyAgent.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.46%. Comparing base (76b2b0a) to head (dedc9cd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5687      +/-   ##
==========================================
- Coverage   93.46%   93.46%   -0.01%     
==========================================
  Files         110      110              
  Lines       38899    38899              
==========================================
- Hits        36358    36356       -2     
- Misses       2541     2543       +2     

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