feat(pm): add phase timings and install summary

[elrrrrrrr]

Summary

Addresses two UX gaps reported during dependency install:

1. The post-resolve clone stage runs clean_deps first (validates & prunes stale node_modules), during which pos doesn't advance and the bar looks frozen on large trees. Now the spinner message reads validating node_modules → linking packages so the user sees which phase is active.
2. The scripts phase had no timing info. Each ✓ line now appends a dimmed [elapsed], and a two-line summary prints at the end of install:

   ✓ 7766/7766 package-lock.json resolved [0.2s]
   ✓ 3550/3550 node_modules cloned [2.6s]
   ✓ 10/10 scripts executed [3.2s]
   
   + 513 added · 3017 reused
   

Implementation notes

• cloner::clone_package now returns Result<bool> (true = freshly materialized, false = valid existing dst reused). Outcomes are accumulated into two process-global atomics exposed via a CloneStats snapshot + Sub impl.
• InstallService::install() snapshots clone_stats() at entry and prints the delta; this keeps nested installs (global install flows) reporting only their own work.
• finish_progress_bar now takes Option<Duration> — one function instead of two + a trampoline. format_elapsed_time is built on a new shared fmt_duration core.

Test plan

• cargo fmt
• cargo clippy -p utoo-pm --all-targets -- -D warnings --no-deps
• cargo test -p utoo-pm --bin utoo (cloner/install/logger tests all green)
• Manual smoke on a large workspace to confirm the summary numbers and timings look sensible

[gemini-code-assist]

Code Review

This pull request enhances the package installation process by adding detailed timing and statistics tracking. It introduces the ability to measure the duration of key phases such as dependency resolution, package linking, and script execution, while also tracking the counts of freshly cloned versus reused packages. A new installation summary is printed upon completion to provide users with these performance metrics. I have no feedback to provide.