dirent: no longer cache the results of Stat and Info

[charlievieth]

This commit changes fastwalk.DirEntry to no longer cache the result of
calling the Stat and Info methods. This reduces memory usage by reducing
the size of the underlying DirEntry type and by saving an allocation in
the call to Stat/Info.

Benchmarks:

goos: darwin
goarch: arm64
cpu: Apple M4 Pro
                           │ base.10.txt │             new.10.txt             │
                           │   sec/op    │   sec/op     vs base               │
UnixDirentInfo/Serial-14     648.6n ± 2%   616.6n ± 1%  -4.92% (p=0.000 n=10)
UnixDirentInfo/Parallel-14   969.4n ± 0%   932.5n ± 0%  -3.81% (p=0.000 n=10)
geomean                      792.9n        758.3n       -4.37%

                           │ base.10.txt │             new.10.txt             │
                           │    B/op     │    B/op     vs base                │
UnixDirentInfo/Serial-14      384.0 ± 0%   336.0 ± 0%  -12.50% (p=0.000 n=10)
UnixDirentInfo/Parallel-14    384.0 ± 0%   336.0 ± 0%  -12.50% (p=0.000 n=10)
geomean                       384.0        336.0       -12.50%

                           │ base.10.txt │             new.10.txt             │
                           │  allocs/op  │ allocs/op   vs base                │
UnixDirentInfo/Serial-14      4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
UnixDirentInfo/Parallel-14    4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
geomean                       4.000        3.000       -25.00%

goos: linux
goarch: arm64
                          │ base.10.txt │             new.10.txt             │
                          │   sec/op    │   sec/op     vs base               │
UnixDirentInfo/Serial-4     425.3n ± 1%   394.3n ± 0%  -7.29% (p=0.000 n=10)
UnixDirentInfo/Parallel-4   248.0n ± 2%   229.8n ± 2%  -7.36% (p=0.000 n=10)
geomean                     324.8n        301.0n       -7.32%

                          │ base.10.txt │             new.10.txt             │
                          │    B/op     │    B/op     vs base                │
UnixDirentInfo/Serial-4      368.0 ± 0%   320.0 ± 0%  -13.04% (p=0.000 n=10)
UnixDirentInfo/Parallel-4    368.0 ± 0%   320.0 ± 0%  -13.04% (p=0.000 n=10)
geomean                      368.0        320.0       -13.04%

                          │ base.10.txt │             new.10.txt             │
                          │  allocs/op  │ allocs/op   vs base                │
UnixDirentInfo/Serial-4      4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
UnixDirentInfo/Parallel-4    4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
geomean                      4.000        3.000       -25.00%

goos: linux
goarch: amd64
cpu: AMD EPYC-Milan Processor
                          │ base.10.txt │             new.10.txt             │
                          │   sec/op    │   sec/op     vs base               │
UnixDirentInfo/Serial-4     2.235µ ± 1%   2.162µ ± 3%  -3.24% (p=0.001 n=10)
UnixDirentInfo/Parallel-4   732.7n ± 2%   695.9n ± 2%  -5.03% (p=0.000 n=10)
geomean                     1.280µ        1.227µ       -4.14%

                          │ base.10.txt │             new.10.txt             │
                          │    B/op     │    B/op     vs base                │
UnixDirentInfo/Serial-4      384.0 ± 0%   336.0 ± 0%  -12.50% (p=0.000 n=10)
UnixDirentInfo/Parallel-4    384.0 ± 0%   336.0 ± 0%  -12.50% (p=0.000 n=10)
geomean                      384.0        336.0       -12.50%

                          │ base.10.txt │             new.10.txt             │
                          │  allocs/op  │ allocs/op   vs base                │
UnixDirentInfo/Serial-4      4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
UnixDirentInfo/Parallel-4    4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
geomean                      4.000        3.000       -25.00%

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.30%. Comparing base (f8029ee) to head (6e67aac).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #71      +/-   ##
==========================================
- Coverage   59.24%   57.30%   -1.94%     
==========================================
  Files          13       13              
  Lines         633      602      -31     
==========================================
- Hits          375      345      -30     
+ Misses        244      243       -1     
  Partials       14       14              

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