perf: parallelize package parsing

[saurabhhhcodes]

Summary

• parallelizes stateless APT search/detail/update parsing with Rayon
• parallelizes pacman installed/update parsing loops
• switches shared alternating two-line package output parsing to par_chunks(2) while preserving score filtering and sorted results
• adds focused parser tests for APT line handling and alternating package output chunking

Notes

rayon is already present in the current dev branch's Cargo.toml, so this PR keeps the dependency set unchanged and applies it to the parsing paths requested in #72.

Validation

• cargo fmt --all -- --check
• cargo test managers -- --nocapture
• cargo test
• cargo clippy --workspace --all-targets --all-features -- -D warnings -A dead_code -A clippy::type_complexity
• git diff --check

Closes #72

[vercel]

Someone is attempting to deploy a commit to the pie's projects Team on Vercel.

A member of the Team first needs to authorize it.

[saurabhhhcodes]

Validation update for #72:

• cargo fmt --all -- --check
• cargo test managers -- --nocapture
• cargo test
• cargo clippy --workspace --all-targets --all-features -- -D warnings -A dead_code -A clippy::type_complexity
• git diff --check

GitHub repo checks are also green: Verify and Build passed. The remaining Vercel status is external team authorization noise, not a Rust/build failure.

If accepted, could you please add the scoring labels from the issue: gssoc:approved, level:intermediate, and type:performance?