fix(mock): improve error message when intercepts are exhausted

[travisbreaks]

Summary

• When all mock intercepts for a request have been consumed, the error message now includes how many interceptors remain and how many were originally defined
• Tracks total registered intercept count via a new kTotalDispatchCount symbol on the dispatches array, so the count persists even after consumed dispatches are cleaned up
• Adds a dedicated test for the "intercepts exhausted" scenario

Before:

MockNotMatchedError: Mock dispatch not matched for path '/foo': subsequent request to origin https://api.example.com was not allowed (net.connect disabled)

After:

MockNotMatchedError: Mock dispatch not matched for path '/foo': subsequent request to origin https://api.example.com was not allowed (net.connect disabled), 0 interceptor(s) remaining out of 3 defined

Fixes #2219

Test plan

• New test should include intercept count in error when intercepts are exhausted verifies the message includes counts after intercepts are consumed
• All existing mock-agent tests updated and passing (99/99)
• All mock-utils tests passing (31/31)
• All mock-pool, mock-client, mock-interceptor, mock-scope tests passing (101/101)
• Lint passes

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.90%. Comparing base (1c5dc1a) to head (5620df1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4912   +/-   ##
=======================================
  Coverage   92.90%   92.90%           
=======================================
  Files         112      112           
  Lines       35638    35645    +7     
=======================================
+ Hits        33108    33116    +8     
+ Misses       2530     2529    -1     

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