refactor: introduce strong types enforcing invariants

[Shadow53]

Resolves #96.

Adds new types and tests representing different types of checksums, paths, and names, that enforce required invariants at parse/creation time.

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[codecov]

Codecov Report

Merging #109 (819e4de) into main (619601f) will increase coverage by 0.82%.
The diff coverage is 95.14%.

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
+ Coverage   89.52%   90.34%   +0.82%     
==========================================
  Files          61       69       +8     
  Lines        4669     4932     +263     
==========================================
+ Hits         4180     4456     +276     
+ Misses        489      476      -13     

Impacted Files	Coverage Δ
src/command/mod.rs	28.57% <0.00%> (ø)
src/config/builder/environment/mod.rs	100.00% <ø> (ø)
src/hoard/mod.rs	0.00% <ø> (ø)
src/hoard/pile_config.rs	100.00% <ø> (ø)
src/lib.rs	100.00% <ø> (ø)
src/checkers/history/operation/v1.rs	69.23% <52.38%> (+16.50%)	⬆️
tests/hoard_diff.rs	87.40% <84.00%> (+0.19%)	⬆️
src/command/diff.rs	71.92% <87.50%> (-0.49%)	⬇️
src/config/builder/envtrie.rs	82.83% <88.18%> (-6.71%)	⬇️
src/env_vars.rs	86.84% <88.46%> (+2.46%)	⬆️
... and 43 more

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