Add Display impl for HRAC and FleetStateChecksum

[fjarri]

• Add Display impl for HRAC and FleetStateChecksum
• Expose it in the bindings as __str__() for Python, and toString() for WASM

[codecov-commenter]

Codecov Report

Merging #22 (a10cb6e) into master (4910d99) will not change coverage.
The diff coverage is 0.00%.

@@          Coverage Diff           @@
##           master     #22   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files          11      11           
  Lines         398     404    +6     
======================================
- Misses        398     404    +6     

Impacted Files	Coverage Δ
nucypher-core/src/fleet_state.rs	0.00% <0.00%> (ø)
nucypher-core/src/hrac.rs	0.00% <0.00%> (ø)

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