implement track reference (tref) box

[bradh]

From ISO/IEC 14496-12:2022 Section 8.3.3

Resolves #117

[coderabbitai]

Walkthrough

Adds support for the tref (track reference) atom across the codebase. A new Tref variant is added to the public Any enum and a tref module is introduced, containing TrackReferenceTypeBox and Tref structs with encode/decode logic and tests. Trak is extended with pub tref: Option<Tref> and the atom nesting configuration is updated to include Tref. Several tests are refactored to replace explicit None initializations with ..Default::default() for struct construction.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 69.23% 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 clearly and concisely describes the main change: implementing the track reference (tref) box, which aligns with the primary objective of the changeset.
Description check	✅ Passed	The description references the ISO/IEC standard specification and resolves issue #117, which is directly related to implementing the tref box.
Linked Issues check	✅ Passed	The PR implements the Track Reference Box (tref) per ISO/IEC 14496-12:2022 Section 8.3.3 as requested in issue #117, with new tref module and struct definitions.
Out of Scope Changes check	✅ Passed	Changes to test files replacing explicit None fields with ..Default::default() are minor refactoring updates compatible with the new tref field addition to Trak.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/moov/trak/tref.rs`:
- Around line 27-37: The decode implementation for TrackReferenceTypeBox must
validate that the payload length is a multiple of 4 before decoding u32 track
IDs: inside fn decode (where Header::decode(buf)? is called and size is
computed) add a check that size % 4 == 0 and return Error::InvalidSize if not,
then compute num_entries = size / 4 and proceed to allocate track_ids and call
u32::decode(buf) for each entry; this prevents leftover bytes from being
misinterpreted as the next header and keeps the existing error type and
variables (track_ids, num_entries, Error::InvalidSize) intact.