Add more Flypack validation and round-trip tests

[primaryNK]

Goal

Improve automated coverage for the versioned .flypack data format.

Flypack files are data-only packages used to store fly identity, cosmetics,
and equipment configuration. Imported data must remain strictly validated and
must not introduce executable content or arbitrary filesystem access.

Suggested test cases

Add deterministic tests for cases such as:

• valid Flypack load/save round-trip
• invalid format version
• missing required fields
• invalid equipment ranges
• NaN or infinity values
• unknown cosmetic or skin IDs
• malformed input
• unexpected extra data
• compatibility with currently supported Flypack versions

Requirements

• Keep .flypack data-only.
• Do not weaken existing validation.
• Do not add DLL, script, shader, or arbitrary path loading.
• Existing tests must continue to pass.

Verification

Run:

build_v068.bat
test_v068_profile_learning.bat