Rust *-unknown-linux-musl builds are statically linked with zero
runtime libc dependency. Detect this pattern in classifyGitHub and
override libc from 'musl' to 'none'. Hard-musl packages (pwsh, bun,
node) use different filename patterns and keep libc='musl'.
Triplet-based resolution with indexed lookup for fast matching.
Supports channel hierarchy (alpha > beta > rc > stable), LTS filtering,
variant selection, format preferences, and arch fallback via CompatArches.
All 13 unit tests and cache integration tests pass against real data
for 100+ packages.
