refactor hvc1 and hev1 to shared implementation, add hvc2 and hev2

[bradh]

I missed the ccst on hev1 the first time around, so its probably better to have a shared implementation. There are more boxes to go in (e.g. lhvC).

Took the opportunity to add hvc2 and hev2 which are the same (at least from https://mpeggroup.github.io/FileFormatConformance/?query=%3D%22hvc2%22 ).

If this works out, I'll do the avc2, avc3, and avc4 in the same way.

[coderabbitai]

Walkthrough

This pull request refactors HEVC atom handling by consolidating four HEVC sample entry types (Hvc1, Hvc2, Hev1, Hev2) through a new define_hevc_sample_entry macro in hvc1.rs. The standalone hev1.rs file is deleted and its implementation is now macro-generated. New variants Hev2 and Hvc2 are added to the Any enum to support additional HEVC codec types. A ccst field is introduced to the Hvcc struct and related test structures. The module exports are updated to remove the separate hev1 module declaration.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely summarizes the main changes: refactoring hvc1 and hev1 into a shared implementation while adding new hvc2 and hev2 variants.
Description check	✅ Passed	The description is directly related to the changeset, explaining the motivation (missed ccst field), the refactoring approach (shared implementation), and future plans.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/moov/trak/mdia/minf/stbl/stsd/hevc/hvc1.rs`:
- Around line 3-70: The match arms in the decode_body of the
define_hevc_sample_entry macro incorrectly use `.into()` to set Option fields
(e.g., hvcc, btrt, colr, pasp, taic, fiel, ccst); replace those assignments with
explicit Some(atom) (e.g., Any::Hvcc(atom) => hvcc = Some(atom)) inside the impl
Atom::decode_body for the generated types so each extracted atom is
idiomatically wrapped in Option; leave the
hvcc.ok_or(Error::MissingBox(Hvcc::KIND)) check as-is and do not change other
logic in encode_body or the Visual/Hvcc fields.