refactor(share/availability): simplify light availability

[walldiss]

• simplification refactoring of Samples selection code
• remove squareSampler
• remove binary encode/decode in favour of json
• removal of no longer relevant TODOs
• rename "cache" naming artefacts from the past
• use height in logs instead of root hash

[renaynay]

Additional request is to move dah validation check in availability.go earlier in the SharesAvailability function -- ideally in the beginning. It doesn't make sense where it currently is.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.16667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 45.33%. Comparing base (2469e7a) to head (8874842).
Report is 369 commits behind head on main.

Files with missing lines	Patch %	Lines
share/availability/light/availability.go	75.00%	2 Missing and 1 partial ⚠️
share/availability/light/sample.go	83.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3895      +/-   ##
==========================================
+ Coverage   44.83%   45.33%   +0.50%     
==========================================
  Files         265      308      +43     
  Lines       14620    21764    +7144     
==========================================
+ Hits         6555     9867    +3312     
- Misses       7313    10844    +3531     
- Partials      752     1053     +301     

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[walldiss]

Had to rebase the PR on main, and commit history is lost. Here is what changed after last reviews

• Removed uneccesary dah validation from both light and full availability
• clean up remaining logs to use height.
• changed uint -> int for Row and Col in Sample