Add KeyMap DAT file support (#617)

[KT053374]

Summary

Implements KeyMap (0x14) parsing in ACE.DatLoader as a focused partial fix for #617.

• Adds KeyMap.cs with support for map names and GUIDs, devices, meta keys, input-map groups, and control bindings.
• Adds collection-count validation, duplicate input-map detection, and malformed-record handling.
• Adds five self-contained regression tests.
• Removes the KeyMap exclusion from UnpackPortalDatFiles_NoExceptions.

Testing

• KeyMapTests: 5 passed, 0 failed.
• UnpackPortalDatFiles_NoExceptions: Passed against End of Retail client_portal.dat in 4 minutes, 28 seconds.
• Both KeyMap records (0x14000000 and 0x14000002) successfully decoded.
• Git whitespace validation passed.

Scope

This PR addresses KeyMap support only. The remaining unsupported file types, RenderMaterial, MaterialModifier, and MaterialInstance, are unchanged.

Partially addresses #617
#617