Serialization of optional values without Clone

[mzabaluev]

With a bit less spiffy syntax, an Option<T> can be serialized without cloning the whole value.

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #1207 (e2dd03f) into main (00401ae) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #1207   +/-   ##
=====================================
  Coverage   64.0%   64.0%           
=====================================
  Files        250     250           
  Lines      21554   21556    +2     
=====================================
+ Hits       13798   13809   +11     
+ Misses      7756    7747    -9     

Impacted Files	Coverage Δ
proto/src/serializers/optional.rs	100.0% <100.0%> (ø)
tendermint/src/node.rs	63.9% <0.0%> (+0.1%)	⬆️
config/src/config.rs	54.9% <0.0%> (+0.1%)	⬆️
testgen/src/header.rs	84.0% <0.0%> (+0.5%)	⬆️
testgen/src/commit.rs	91.3% <0.0%> (+0.6%)	⬆️
light-client-verifier/src/types.rs	39.3% <0.0%> (+0.8%)	⬆️
testgen/src/vote.rs	85.7% <0.0%> (+1.6%)	⬆️

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