chore(ci): run e2e tests in parallel

[janisz]

Description

Speedup e2e tests by running in parallel and optimising cache key.

Validation

CI

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.88%. Comparing base (9bf4946) to head (0b62c73).
⚠️ Report is 11 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
- Coverage   78.37%   73.88%   -4.49%     
==========================================
  Files          27       30       +3     
  Lines        1216     1302      +86     
==========================================
+ Hits          953      962       +9     
- Misses        223      300      +77     
  Partials       40       40              

Flag	Coverage Δ
integration	73.88% <ø> (?)
unit	73.88% <ø> (?)

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[github-actions]

E2E Test Results - ❌ Job Failed

Commit: 0b62c73
Workflow Run: View Details
Artifacts: Download test results & logs

[janisz]

It's blocked by:

• Race condition in MCP client causes nil pointer panic during parallel execution mcpchecker/mcpchecker#259