Added & implemented Indexable trait for Context;

[marvin-hansen]

Describe your changes

• Added Indexable trait ;
• Implemented Indexable trait for Context;
• Documented all protocols / traits in deep causality crate

Code checklist before requesting a review

• I have signed the DCO?
• All tests are passing when running make test?
• No errors or security vulnerabilities are reported by make check?

For details on make, please see BUILD.md

Note: The CI runs all of the above and fixing things before they hit CI speeds
up the review and merge process. Thank you.

[codecov]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (7b91bd8) 88.22% compared to head (88a791f) 87.85%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
...src/types/context_types/context_graph/indexable.rs	0.00%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
- Coverage   88.22%   87.85%   -0.38%     
==========================================
  Files         122      123       +1     
  Lines        3219     3235      +16     
==========================================
+ Hits         2840     2842       +2     
- Misses        379      393      +14     

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