chore(format): use capsule-type serialization for fs nodes

[appcypher]

Summary

Share payloads already serialize to the capsule-type format as part of the stabilization goals of wnfs but the filesystem nodes still serialize to old format.

This PR implements said serialization format for private and public nodes.

Test plan (required)

scripts/rs-wnfs.sh test

Closing issues

Closes #248

[codecov]

Codecov Report

Merging #265 (23f9ba0) into main (5ed87fe) will decrease coverage by 1.86%.
The diff coverage is 60.68%.

@@            Coverage Diff             @@
##             main     #265      +/-   ##
==========================================
- Coverage   61.92%   60.06%   -1.86%     
==========================================
  Files          35       38       +3     
  Lines        2676     2697      +21     
  Branches      657      666       +9     
==========================================
- Hits         1657     1620      -37     
- Misses        563      624      +61     
+ Partials      456      453       -3     

Impacted Files	Coverage Δ
wnfs/examples/privateref.rs	0.00% <0.00%> (ø)
wnfs/src/private/encrypted.rs	66.66% <0.00%> (+4.16%)	⬆️
wnfs/src/private/node/header.rs	85.48% <0.00%> (-1.19%)	⬇️
wnfs/src/private/node/serializable.rs	0.00% <0.00%> (ø)
wnfs/src/private/share.rs	64.49% <0.00%> (+0.25%)	⬆️
wnfs/src/public/node/serializable.rs	0.00% <0.00%> (ø)
wnfs/src/public/node/node.rs	51.35% <42.85%> (ø)
wnfs/src/private/node/node.rs	65.18% <55.55%> (+3.28%)	⬆️
wnfs/src/public/directory.rs	70.42% <68.75%> (+0.15%)	⬆️
wnfs/src/private/directory.rs	67.84% <69.69%> (-3.98%)	⬇️
... and 3 more

... and 7 files with indirect coverage changes

[matheus23]

This is great! Thank you :)