test(frontend): add unit tests for serializePortIdentity

[rbelavadi]

What changes were proposed in this PR?

Adds port-identity-serde.spec.ts to cover serializePortIdentity, a previously untested pure utility function in common/util/ that serializes a PortIdentity into the stable string key id_internal.

This format is one half of a cross-language contract: the backend produces the identical string in PortIdentityKeySerializer.portIdToString and reads it back by splitting on "_" in PortIdentityKeyDeserializer. A format mismatch on either side would cause the frontend's schema lookup to silently return undefined rather than fail, so the exact output is worth pinning.

Covers four groups of behavior:

• Format: exact key for external and internal ports, including the id: 0 falsy-number boundary and large and negative ids passing through unvalidated. These mirror PortIdentityKeySerializerSpec.scala's case table exactly, so both ends of the contract are now pinned by matching assertions.
• Distinctness: ports differing only by id, or only by internal, cannot collide on the same key.
• Stability: equal inputs always serialize identically.
• Real usage: the key works for object lookup when generated independently at write and read time, and remains splittable into exactly two fields for the backend deserializer.

No production code was changed.

Any related issues, documentation, discussions?

Closes #6631

How was this PR tested?

Added 12 new unit tests in port-identity-serde.spec.ts covering all behavior described in the issue. Ran locally via ng test --include src/app/common/util/port-identity-serde.spec.ts --watch=false; all 12 pass. Full suite also green via yarn test (3817 passed, 2 skipped, 198 files).

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Claude Opus 4.8)

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• No candidates found from git blame history.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.91%. Comparing base (a351f44) to head (84bf928).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6938      +/-   ##
============================================
+ Coverage     77.30%   82.91%   +5.60%     
============================================
  Files          1161      328     -833     
  Lines         45922    20135   -25787     
  Branches       5101     2905    -2196     
============================================
- Hits          35501    16695   -18806     
+ Misses         8840     2775    -6065     
+ Partials       1581      665     -916     

Flag	Coverage Δ
access-control-service	?
agent-service	?
amber	?
computing-unit-managing-service	?
config-service	?
file-service	?
frontend	82.91% <ø> (+0.33%)	⬆️
notebook-migration-service	?
pyamber	?
workflow-compiling-service	?

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[rbelavadi]

/request-review @Ma77Ball

[xuang7]

LGTM!