Feat: add Serde as codec feature

[mrLSD]

Description

➡️ Added Serde serializer, which can be enabled via codec feature flag:

• [Feature]: Implement Serde serializer #21

➡️ Extended README.
➡️ Extended tests

💠 It's most useful for:

• ➡️ AST - AST can be presented with (se/dese)rialization.
• ➡️ State - whole state as serialization result
• ➡️ SematicStack - serialized instructions set

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (177e077) 100.00% compared to head (b75703e) 99.54%.

Files	Patch %	Lines
src/ast.rs	92.45%	8 Missing ⚠️
src/types/block_state.rs	95.83%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##            master      #23      +/-   ##
===========================================
- Coverage   100.00%   99.54%   -0.46%     
===========================================
  Files            9        9              
  Lines         1789     1975     +186     
===========================================
+ Hits          1789     1966     +177     
- Misses           0        9       +9     

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