Abstract big integer representation for hints

[fmoletta]

Across multiple hints, structs are used to represent big integers, all consisting of a set of Felts of varying size. The logic is the same for all structs, so it doesn't make sense to implement it for each struct separately. As we don't have const generics i go, we can't really make a generic structure to represent all of these types, but we can abstract the logic of each method into functions operating over a slice of Felts. And implement wrappers for each type using these methods What this Pr does:

• Add functions that operate over the limbs []Felt (fromBaseAddr, fromVarName, Pack, Pack86, Split, Insert)
• Implement a BigInt3 wrapper using these methods and replace the current implementation

[codecov-commenter]

Codecov Report

Merging #283 (cddf2db) into main (102682a) will decrease coverage by 0.76%. The diff coverage is 28.57%.

@@            Coverage Diff             @@
##             main     #283      +/-   ##
==========================================
- Coverage   58.75%   57.99%   -0.76%     
==========================================
  Files          42       43       +1     
  Lines        5383     5419      +36     
==========================================
- Hits         3163     3143      -20     
- Misses       1947     2003      +56     
  Partials      273      273              

Files Changed	Coverage Δ
pkg/hints/hint_utils/bigint_utils.go	0.00% <0.00%> (ø)
pkg/hints/ec_hint.go	62.88% <100.00%> (-3.50%)	:arrow_down:
pkg/hints/hint_processor.go	98.34% <100.00%> (ø)

... and 1 file with indirect coverage changes

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