perf(pm): bound concurrent package clones

[killagu]

Summary

• bound concurrent package clone/hardlink/copy work in utoo-pm cloner
• reduce warm-link blocking pool and filesystem contention observed in pm-bench

Validation

• cargo build --profile release-local -p utoo-pm
• cargo test -p utoo-pm cloner
• cargo test -p utoo-pm
• cargo fmt --check
• cargo clippy -p utoo-pm --all-targets -- -D warnings
• git diff --check HEAD~1..HEAD

Issue: EGG-20

[gemini-code-assist]

Code Review

This pull request introduces a concurrency limit for filesystem clone operations in crates/pm/src/util/cloner.rs by implementing a tokio::sync::Semaphore. The limit is dynamically calculated based on available parallelism to mitigate scheduler churn and filesystem contention. Feedback suggests moving the semaphore acquisition to encompass the remove_dir_all operation, as it is a heavy filesystem task that could contribute to the contention the PR aims to prevent.

[Copilot]

Pull request overview

Bounds concurrent package clone/hardlink/copy work in utoo-pm to reduce blocking-pool scheduling churn and filesystem contention during installs (notably warm-link scenarios).

Changes:

• Introduced a process-wide semaphore to limit concurrent filesystem clone operations.
• Added a helper to derive the clone concurrency limit from available parallelism.