Prepare v0.11.3 safety and compression improvements

[wefalltomorrow]

Summary

Prepare Compactor 0.11.3 with targeted safety, accounting, memory, estimation, and compression-policy improvements informed by the upstream issue feedback and review of trash-compactor and CompactGUI.

Compression and responsiveness

• Make LZX Auto conservative: 1 worker on CPUs with <=4 physical cores and at most 2 workers on larger CPUs
• Respect an explicit manual thread limit for LZX as an intentional override; the HDD single-thread safeguard still applies when enabled
• Keep XPRESS modes free to scale to the configured worker limit
• Add selectable compression/decompression worker priority: Lowest, Below Normal, Normal, Above Normal, Highest
• Default worker priority to Below Normal while leaving the GUI and analysis threads at normal priority
• Prevent system sleep during compression/decompression without forcing the display awake

File-update safety

• Allow readers while denying concurrent writers/deleters during active WOF operations
• Read size/mtime from the already-open protected file handle before reusing analysis estimates

Analysis, accounting, and memory

• Detect actual NTFS cluster size
• Skip files that cannot save an allocation cluster
• Separate logical size from physical allocation correctly
• Make displayed projections algorithm- and cluster-aware while keeping eligibility based on the raw sampled result
• Bound parallel estimation candidates to 4096 files
• Avoid retaining every skipped path on huge scans
• Measure actual post-decompression allocation

Target safety

• Require local NTFS folder targets
• Reject network/UNC targets and whole-drive roots
• Protect the active Windows directory, System Volume Information, root $* directories, and root Recovery
• Reject legacy LZNT1-compressed target folders
• Warn when DirectStorage runtimes are detected

Maintenance

• Repair Cargo.lock so dependency checksums remain identical to the known-good v0.11.2 lockfile and only the local package version changes
• Document the new v0.11.3 behavior

This is intentionally kept focused: no schedulers, background services/watchers, Steam databases, extension blacklists, CompactOS/whole-drive features, telemetry, Python runtime, or automatic per-file algorithm selection.