Preserve wheel filenames using embed.FS for PEP 427 compliance
pip requires wheel filenames to follow PEP 427 format (e.g.,
cog-0.16.10-py3-none-any.whl). Previously we renamed wheels to simple
names (cog.whl) which pip rejected.
Switch from []byte embedding to embed.FS which preserves the original
versioned filenames. Panic instead of returning error since missing
wheels indicate a broken build.
