Accept FootstepSet DATA longer than its counts

[Avick3110]

A FootstepSet whose DATA is longer than 4 bytes per FormID counted in XCNT fails to parse with DATA record had unexpected length that did not match previous counts, through both the direct parse and the overlay. The record that hit this, in Skyrim, has XCNT 0, 0, 0, 0, 0 and DATA 00 00 00 00. xEdit sizes each DATA array from its XCNT count and shows the leftover bytes as unused data, and the game reads by the counts too, so both load it.

The fix, applied alike to Skyrim, Fallout 4 and Starfield:

• A DATA longer than its counts is accepted. Both readers read each list by its count, then move to the end of DATA, so the surplus bytes are skipped and the next subrecord is read from the right place.
• A DATA shorter than its counts still throws the same error as before.
• A DATA whose length runs past the end of its record throws.
• The public GetListCounts(IMutagenReadStream) keeps its signature. It calls an internal overload that also returns where DATA ends.
• Writing is unchanged, so a re-save drops the surplus. No generated code changes.

Tests in FootstepSetDataLengthTests, each read through the direct parser and the overlay. Skyrim: zero counts with surplus, a populated list with surplus (including surplus that is not a multiple of 4) followed by EDID, a short DATA that throws, a DATA length past the record end that throws, and a matching record that writes back byte-identical. Fallout 4 and Starfield: a populated list with surplus. The surplus tests fail on dev. Mutagen.Bethesda.UnitTests passes on net9.0 and net10.0. Passthrough tests against real game data were not run; could you run them on Skyrim, Fallout 4 and Starfield?

I found this through houseCARL, a tool built on Mutagen, which could not read a Skyrim FootstepSet carrying surplus DATA bytes (Avick3110/houseCARL#1037).

🤖 Generated with Claude Code