Remove unecessary conversion functions between Felt & BigUint/BigInt

[fmoletta]

Closes #1495

[github-actions]

Benchmark Results for unmodified programs 🚀

Command	Mean [s]	Min [s]	Max [s]	Relative
base big_factorial	2.260 ± 0.007	2.247	2.272	1.00
head big_factorial	2.267 ± 0.016	2.244	2.303	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base big_fibonacci	2.243 ± 0.012	2.230	2.263	1.00 ± 0.01
head big_fibonacci	2.241 ± 0.013	2.230	2.267	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base blake2s_integration_benchmark	8.259 ± 0.072	8.178	8.360	1.00
head blake2s_integration_benchmark	8.299 ± 0.151	8.217	8.711	1.00 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base compare_arrays_200000	2.295 ± 0.014	2.278	2.315	1.00
head compare_arrays_200000	2.302 ± 0.019	2.283	2.352	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base dict_integration_benchmark	1.457 ± 0.004	1.452	1.464	1.00
head dict_integration_benchmark	1.459 ± 0.005	1.453	1.470	1.00 ± 0.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base field_arithmetic_get_square_benchmark	1.296 ± 0.023	1.284	1.359	1.00 ± 0.02
head field_arithmetic_get_square_benchmark	1.291 ± 0.007	1.285	1.307	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base integration_builtins	8.286 ± 0.094	8.197	8.496	1.00 ± 0.01
head integration_builtins	8.272 ± 0.046	8.216	8.338	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base keccak_integration_benchmark	8.518 ± 0.059	8.457	8.602	1.00
head keccak_integration_benchmark	8.527 ± 0.045	8.470	8.609	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base linear_search	2.330 ± 0.013	2.311	2.347	1.00
head linear_search	2.341 ± 0.020	2.322	2.385	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base math_cmp_and_pow_integration_benchmark	1.573 ± 0.004	1.568	1.580	1.00 ± 0.00
head math_cmp_and_pow_integration_benchmark	1.571 ± 0.003	1.566	1.575	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base math_integration_benchmark	1.450 ± 0.013	1.437	1.475	1.01 ± 0.01
head math_integration_benchmark	1.440 ± 0.006	1.430	1.449	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base memory_integration_benchmark	1.265 ± 0.020	1.254	1.320	1.00
head memory_integration_benchmark	1.270 ± 0.022	1.254	1.327	1.00 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base operations_with_data_structures_benchmarks	1.604 ± 0.006	1.596	1.615	1.00
head operations_with_data_structures_benchmarks	1.616 ± 0.023	1.598	1.670	1.01 ± 0.01

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base pedersen	605.6 ± 1.4	604.1	609.2	1.00
head pedersen	605.7 ± 1.9	603.0	609.0	1.00 ± 0.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base poseidon_integration_benchmark	1.070 ± 0.003	1.065	1.074	1.00 ± 0.01
head poseidon_integration_benchmark	1.068 ± 0.005	1.061	1.075	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base secp_integration_benchmark	1.932 ± 0.006	1.923	1.943	1.00 ± 0.00
head secp_integration_benchmark	1.929 ± 0.006	1.920	1.938	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base set_integration_benchmark	750.7 ± 2.2	747.2	754.8	1.00
head set_integration_benchmark	751.5 ± 5.1	748.4	765.2	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base uint256_integration_benchmark	4.540 ± 0.025	4.513	4.586	1.00
head uint256_integration_benchmark	4.560 ± 0.048	4.517	4.675	1.00 ± 0.01

[Oppen]

Nice cleanup. There's some slowdown that may be worth investigating.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (0ea638f) 97.12% compared to head (8385994) 97.13%.

Files	Patch %	Lines
...int_processor/builtin_hint_processor/math_utils.rs	84.84%	5 Missing ⚠️
...sor/cairo_1_hint_processor/hint_processor_utils.rs	40.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1562   +/-   ##
=======================================
  Coverage   97.12%   97.13%           
=======================================
  Files          91       91           
  Lines       37245    37263   +18     
=======================================
+ Hits        36175    36196   +21     
+ Misses       1070     1067    -3     

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