fix(hang): omit empty HEVC constraint component in codec string

[quidamschwarz]

Fixes #1780.

HEVC streams whose general_constraint_indicator_flags are all zero produced a codec string ending
in a dangling . (e.g. hvc1.1.60.L150.), which H265::from_str then rejected while parsing the
empty trailing field as a hex int. This breaks the catalog round-trip for such streams — both
catalog generation on publish and subscribe_catalog/subscribe_media on consume (surfaces to
callers as json: expected int). All-zero constraint flags are common in live HEVC from hardware
encoders, so it's hit publishing a real camera via moq-cli … publish … fmp4.

Changes — rs/hang/src/catalog/video/h265.rs

• Display: emit the constraint component (and its leading .) only when there are significant
  bytes, so all-zero flags yield hvc1.1.60.L150 instead of hvc1.1.60.L150..
• FromStr: tolerate an empty trailing field, so streams already published with the dangling
  . still parse (version skew while producers update).
• Test: test_h265_zero_constraints (zero-constraint round-trip + dangling-. parse). The
  existing test_h265 / test_h265_long / test_h265_out_of_band cases are unchanged.

cargo test -p hang passes (4/4 in the h265 module).

[kixelated]

thanks, I'll fix the unrelated CI failure

[coderabbitai]

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Reviewing files that changed from the base of the PR and between eb67c18 and 3f230d6.

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• rs/hang/src/catalog/video/h265.rs

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Walkthrough

The H265 codec string implementation in h265.rs is updated in two ways. The Display implementation now checks whether all constraint_flags bytes are zero and, if so, omits the constraints component entirely from the formatted string instead of appending a trailing .. The FromStr parser is updated to skip empty tokens in the constraint-parsing loop, making it tolerant of a dangling . produced by older encoders or muxers. A new unit test verifies round-trip correctness for an all-zero-constraints codec string in both the omitted form and the legacy dangling-dot form.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: fixing the omission of empty HEVC constraint component in codec strings, which is the core issue addressed in the changeset.
Description check	✅ Passed	The description is well-related to the changeset, explaining the problem (dangling period in codec strings), the root cause, and the solution implemented in the code.
Linked Issues check	✅ Passed	The PR fully addresses issue #1780's objectives: the Display implementation now omits the constraint component when all bytes are zero, FromStr tolerates empty trailing fields, and test coverage for zero-constraint scenarios was added.
Out of Scope Changes check	✅ Passed	All changes in the PR are directly scoped to resolving issue #1780, focusing exclusively on the H265 constraint flags handling in the codec string Display and parsing logic.

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