ReadMetadata used io.LimitReader which silently truncated responses at
the size limit. For packages like drizzle-orm (~92MB metadata), this
produced invalid JSON that was served to clients.
Now returns ErrMetadataTooLarge when the limit is exceeded, and bumps
the limit from 50MB to 100MB.
Fixes#78
POST endpoints (/api/outdated, /api/bulk) now reject bodies over 1 MB
using http.MaxBytesReader. Upstream metadata reads (npm, pypi, composer,
nuget, pub) now use io.LimitReader capped at 50 MB to prevent OOM from
unexpectedly large responses.
