Implement simple caching for -fstype

[nerdroychan]

Fix #418.

Before:

Benchmark 1: find ~/Workspace -fstype xfs
  Time (mean ± σ):     195.8 ms ±   3.2 ms    [User: 34.7 ms, System: 160.7 ms]
  Range (min … max):   192.4 ms … 202.4 ms    14 runs

Benchmark 2: target/release/find ~/Workspace -fstype xfs
  Time (mean ± σ):     12.494 s ±  0.098 s    [User: 2.645 s, System: 8.936 s]
  Range (min … max):   12.318 s … 12.670 s    10 runs

Summary
  find ~/Workspace -fstype xfs ran
   63.80 ± 1.16 times faster than target/release/find ~/Workspace -fstype xfs

After:

Benchmark 1: find ~/Workspace -fstype xfs
  Time (mean ± σ):     190.7 ms ±   3.4 ms    [User: 30.6 ms, System: 159.8 ms]
  Range (min … max):   186.9 ms … 198.0 ms    15 runs

Benchmark 2: target/release/find ~/Workspace -fstype xfs
  Time (mean ± σ):     284.1 ms ±   3.2 ms    [User: 67.8 ms, System: 215.7 ms]
  Range (min … max):   278.7 ms … 289.0 ms    10 runs

Summary
  find ~/Workspace -fstype xfs ran
    1.49 ± 0.03 times faster than target/release/find ~/Workspace -fstype xfs

Not exactly as fast, but significantly faster than no caching.

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.

Project coverage is 65.84%. Comparing base (7f4423e) to head (4ae5e27).

Files	Patch %	Lines
src/find/matchers/fs.rs	84.61%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #419      +/-   ##
==========================================
+ Coverage   65.51%   65.84%   +0.32%     
==========================================
  Files          34       34              
  Lines        3953     3970      +17     
  Branches      906      907       +1     
==========================================
+ Hits         2590     2614      +24     
  Misses        998      998              
+ Partials      365      358       -7     

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[hanbings]

Merged. great optimization, thanks!