implement ainf box.

[bradh]

This is from https://www.uvcentral.com/files/CFFMediaFormat-2_2.pdf Section E.1.1.2 Its in the MPEG file format conformance data, but appears to be legacy in DECE.

Resolves #121

[coderabbitai]

Walkthrough

The PR adds support for the AINF atom extension to the codebase. A new Ainf variant is added to the Any enum, and a new module implements an Ainf struct with fields for hidden, profile_version, and apid, along with trait implementations for decoding and encoding AINF atoms. The Moov struct is updated to include an optional ainf field. Test files are updated to use default field initialization patterns instead of explicit field assignments.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'implement ainf box' directly and clearly describes the main change—adding a new ainf box implementation across multiple files.
Description check	✅ Passed	The description is related to the changeset, referencing the AINF box specification and linking to the corresponding issue (#121), though it provides minimal technical detail.
Docstring Coverage	✅ Passed	Docstring coverage is 81.82% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

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[kixelated]

#112 ?

[bradh]

Possibly, but I'm more interested in flagging this case because the spec says there can be nested boxes, rather than just padding.

Does make me think that up to 8 bytes would be a valid skip case for #112, while this is more "at least a Box" size.