fix: Public conflict reconciliation edge case on files with equal content but different metadata

[matheus23]

This

• improves the proptest setup to generate more diverse file system cases
• fixes a bug where files with equal content but different metadata would not merge commutatively
• factors out the PublicFile::merge function from PublicDirectory::merge_helper

[codecov]

Codecov Report

Attention: Patch coverage is 57.50000% with 17 lines in your changes are missing coverage. Please review.

Project coverage is 54.98%. Comparing base (dc0785a) to head (0a7f9f7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #430      +/-   ##
==========================================
+ Coverage   54.43%   54.98%   +0.54%     
==========================================
  Files          57       57              
  Lines        4126     4156      +30     
  Branches     1028     1036       +8     
==========================================
+ Hits         2246     2285      +39     
+ Misses       1221     1196      -25     
- Partials      659      675      +16     

Files	Coverage Δ
wnfs/src/private/directory.rs	68.92% <ø> (ø)
wnfs/src/private/file.rs	70.11% <100.00%> (ø)
wnfs/src/public/node/node.rs	66.07% <ø> (ø)
wnfs/examples/tiered_blockstores.rs	0.00% <0.00%> (ø)
wnfs/src/public/directory.rs	68.53% <45.45%> (+4.27%)	⬆️
wnfs/src/public/file.rs	63.46% <62.96%> (+3.46%)	⬆️

... and 2 files with indirect coverage changes