cache implied directory parent during unpack

[crazy-max]

Avoid repeated parent directory checks for consecutive archive entries that share the same implicit parent.

Clear the cache after extraction-side removals so whiteouts and replacements cannot reuse stale parent state. Add a whiteout regression test and benchmarks for the implied-directory path.

$ go test . -run ^$ -bench BenchmarkCreateImpliedDirectoriesSameParent -benchmem -count=5
goos: darwin
goarch: arm64
pkg: github.com/moby/go-archive
cpu: Apple M3 Max
BenchmarkCreateImpliedDirectoriesSameParent/uncached-14                    66552             15672 ns/op             271 B/op          5 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/uncached-14                    70644             16508 ns/op             271 B/op          5 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/uncached-14                    74014             16599 ns/op             271 B/op          5 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/uncached-14                    73827             16483 ns/op             271 B/op          5 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/uncached-14                    73699             16613 ns/op             271 B/op          5 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/cached-14                   48969264                24.03 ns/op            0 B/op          0 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/cached-14                   48283262                23.91 ns/op            0 B/op          0 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/cached-14                   49352673                24.08 ns/op            0 B/op          0 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/cached-14                   50833365                24.04 ns/op            0 B/op          0 allocs/op
BenchmarkCreateImpliedDirectoriesSameParent/cached-14                   50965332                23.81 ns/op            0 B/op          0 allocs/op
PASS
ok      github.com/moby/go-archive      13.154s

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.35%. Comparing base (e738eed) to head (8f8d61d).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
diff.go	57.14%	1 Missing and 2 partials ⚠️
archive.go	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
+ Coverage   65.25%   65.35%   +0.10%     
==========================================
  Files          46       46              
  Lines        2377     2390      +13     
==========================================
+ Hits         1551     1562      +11     
  Misses        606      606              
- Partials      220      222       +2     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[vvoland]

While reviewing I thought about a bit simpler solution without having to maintain the mutable cache.. See #113. Let me know if it looks better to you as well