pki: add fuzzer

[AdamKorcz]

Signed-off-by: AdamKorcz adam@adalogics.com

Summary

Adds a fuzzer that tests the public key APIs and the signature APIs.

With the public key APIs it:

1. Creates a public key
2. Gets the canonical value
3. Creates another public key with the canonical value

With the signature APIs it:

1. Creates a signature
2. Gets the canonical value
3. Creates another signature with the canonical value
4. Verifies some test data.

Release Note

Documentation

[codecov-commenter]

Codecov Report

Merging #1256 (345e656) into main (042ae08) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1256      +/-   ##
==========================================
+ Coverage   63.19%   63.23%   +0.03%     
==========================================
  Files          82       82              
  Lines        7670     7670              
==========================================
+ Hits         4847     4850       +3     
+ Misses       2210     2208       -2     
+ Partials      613      612       -1     

Flag	Coverage Δ
e2etests	47.74% <ø> (ø)
unittests	42.08% <ø> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/types/rekord/v0.0.1/entry.go	67.76% <0.00%> (-0.66%)	⬇️
pkg/types/tuf/v0.0.1/entry.go	49.79% <0.00%> (+0.81%)	⬆️
pkg/types/alpine/v0.0.1/entry.go	73.57% <0.00%> (+1.21%)	⬆️

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