Use custom (de)serialization for SessionStaticKey into bytes

[derekpierre]

Type of PR:

• Bugfix
• Feature
• Documentation
• Other

Required reviews:

• 1
• 2
• 3

What this does:
SessionStaticKey protocol objects had varied lengths due to serialization to vector of integers instead of bytestrings. This fixes that.

Issues fixed/closed:

• Fixes #...

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network.
E.g., if this PR address a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

What should reviewers focus on?
Is there a particular commit/function/section of your PR that requires more attention from reviewers?

[codecov-commenter]

Codecov Report

Merging #63 (8dcdcd2) into main (830dc68) will increase coverage by 1.24%.
The diff coverage is 97.50%.

@@            Coverage Diff             @@
##             main      #63      +/-   ##
==========================================
+ Coverage   19.50%   20.75%   +1.24%     
==========================================
  Files          17       17              
  Lines        3214     3252      +38     
==========================================
+ Hits          627      675      +48     
+ Misses       2587     2577      -10     

Impacted Files	Coverage Δ
nucypher-core/src/dkg.rs	89.61% <97.50%> (+3.07%)	⬆️

[derekpierre]

@fjarri I wasn't able to get serdect to act any differently when using serialize_hex_lower_or_bin/deserialize_hex_or_bin but I was able to get the byte serialization working using serde_bytes.

Result of test in nucypher using updated code:

>>>>> key-length: 42
>>>>> key-length: 42
>>>>> key-length: 42
>>>>> key-length: 42