refactor(integration): remove legacy test infrastructure

[hubcio]

TestServer, ClientFactory, and protocol-specific client factories
duplicated functionality now provided by TestHarness and the
iggy_harness proc macro.

Changes:

• Delete ~2000 lines of deprecated test utilities
• Migrate all tests to unified TestHarness API
• Move TLS cert generation into ServerHandle
• Add port binding verification on server startup
• Update BDD, CLI, and server scenario tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.51%. Comparing base (d98176a) to head (178d278).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2678      +/-   ##
==========================================
- Coverage   69.80%   69.51%   -0.30%     
==========================================
  Files         568      568              
  Lines       55238    55238              
  Branches    55238    55238              
==========================================
- Hits        38560    38398     -162     
- Misses      14799    14961     +162     
  Partials     1879     1879              

Flag	Coverage Δ
rust	69.51% <100.00%> (-0.30%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ore/server/src/websocket/websocket_tls_listener.rs	70.34% <100.00%> (+2.06%)	⬆️

... and 16 files with indirect coverage changes

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