fix: parse JSON output from func run in E2E tests

[Kunal1522]

Fixes #3199

Modified E2E tests to use --json flag and parse output for function address instead of manually choosing ports. This prevents test failures when the chosen port is already in use.

Changes:

• Added parseRunJSON helper to eliminate code duplication
• Modified TestCore_Run,TestCore_Invoke,TestMatrix_Run to use JSON output parsing
• Removed chooseOpenAddress usage in favor of --json flag

Tests now work reliably even when default ports (8080) are busy.

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[knative-prow]

Hi @Kunal1522. Thanks for your PR.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.34%. Comparing base (039b926) to head (50488cb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3320      +/-   ##
==========================================
- Coverage   55.09%   54.34%   -0.76%     
==========================================
  Files         170      170              
  Lines       19850    19850              
==========================================
- Hits        10937    10788     -149     
- Misses       7845     8030     +185     
+ Partials     1068     1032      -36     

Flag	Coverage Δ
e2e	39.53% <ø> (-0.07%)	⬇️
e2e go	35.67% <ø> (+0.05%)	⬆️
e2e node	31.30% <ø> (+0.16%)	⬆️
e2e python	31.39% <ø> (-3.97%)	⬇️
e2e quarkus	31.45% <ø> (+0.16%)	⬆️
e2e rust	30.91% <ø> (+0.17%)	⬆️
e2e springboot	30.91% <ø> (+0.14%)	⬆️
e2e typescript	31.41% <ø> (+0.16%)	⬆️
integration	17.49% <ø> (ø)
unit macos-14	44.96% <ø> (ø)
unit macos-latest	44.96% <ø> (ø)
unit ubuntu-24.04-arm	45.07% <ø> (ø)
unit ubuntu-latest	45.86% <ø> (ø)
unit windows-latest	44.98% <ø> (ø)

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