Improved path challenge handling.

[rthalley]

1. We are willing to reply to up to 5 outstanding challenges on a connection, as it is legal for a client to send more than one. We limit to 5 to prevent excessive challenging.

2. We now accept path challege responses on any network path, in accordance with RFC 9000 section 8.2.3.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (6c5b9db) to head (77014f8).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #483   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           25        25           
  Lines         4976      4987   +11     
=========================================
+ Hits          4976      4987   +11     

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[rthalley]

This patch addresses the issue raised by [#189], though with a different implementation. It also addresses another issue, which is that we may need to reply to more than one remote challenge on the same path. Both sides are bounded, currently to 5 items, to avoid any possible resource attack. There are tests and coverage remains at 100%.

[rthalley]

I will lint this one further and push an update tonight or tomorrow morning