Merge unsigned() and signed() search strategies into felts() strategy

[mkaput]

This PR replaces the unsigned() and signed() fuzzing search strategies with a new (and now default) search strategy called simply felts().

From Cairo code perspective, both strategies observed the same range of values, due to the modulo arithmetic of felts. The only difference between these two strategies laid in a method how input values were picked.

I did a bunch of benchmarks and I have concluded that exploring felts in range MIN_FELT...MAX_FELT made Hypothesis pick more variadic set of values. signed() explored almost always around 30% more distinct values than unsigned().

Therefore, the felts() strategy has the same behaviour as former signed().

fix #597

[codecov[bot]]

Codecov Report

Merging #601 (2ae08d8) into master (ac36eb1) will increase coverage by 0.02%. The diff coverage is 91.11%.

@@            Coverage Diff             @@
##           master     #601      +/-   ##
==========================================
+ Coverage   82.72%   82.74%   +0.02%     
==========================================
  Files         189      190       +1     
  Lines        6279     6282       +3     
==========================================
+ Hits         5194     5198       +4     
+ Misses       1085     1084       -1     

Impacted Files	Coverage Δ
...ostar/commands/test/fuzzing/strategies/integers.py	78.57% <78.57%> (ø)
...rotostar/commands/test/fuzzing/strategies/felts.py	91.66% <91.66%> (ø)
...ostar/commands/test/fuzzing/strategies/__init__.py	83.33% <100.00%> (+1.51%)	:arrow_up:
...otostar/commands/test/fuzzing/strategy_selector.py	100.00% <100.00%> (ø)
...ar/commands/test/fuzzing/strategy_selector_test.py	100.00% <100.00%> (ø)

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