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]

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.50%. Comparing base (49f9e2c) to head (99a9306).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6938      +/-   ##
============================================
- Coverage     78.96%   78.50%   -0.46%     
+ Complexity     3798     3715      -83     
============================================
  Files          1161     1161              
  Lines         46084    46036      -48     
  Branches       5110     5102       -8     
============================================
- Hits          36388    36139     -249     
- Misses         8076     8291     +215     
+ Partials       1620     1606      -14     

Flag	Coverage Δ		*Carryforward flag
access-control-service	70.00% <ø> (ø)		Carriedforward from 4af3a85
agent-service	76.76% <ø> (ø)		Carriedforward from 4af3a85
amber	71.48% <ø> (-0.75%)	⬇️	Carriedforward from 4af3a85
computing-unit-managing-service	20.49% <ø> (ø)		Carriedforward from 4af3a85
config-service	66.66% <ø> (ø)		Carriedforward from 4af3a85
file-service	67.21% <ø> (ø)		Carriedforward from 4af3a85
frontend	82.91% <ø> (-0.01%)	⬇️
notebook-migration-service	78.94% <ø> (ø)		Carriedforward from 4af3a85
pyamber	93.54% <ø> (-1.85%)	⬇️	Carriedforward from 4af3a85
workflow-compiling-service	55.14% <ø> (ø)		Carriedforward from 4af3a85

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[rbelavadi]

/request-review @Ma77Ball

[xuang7]

LGTM!