fix: rsa key generation

[MarcosNicolau]

Description
Fixes some rsa key generation bugs related to the management of the biguint sizes, some operations were overflowing because we were not allocating enough space.

Key generation test has been modified to verify the RSA premise:

Given three larger integers e,d,n such that for every integer $0 \le m \le n$:
$(m^e)^d \equiv m \mod n$

[github-actions]

Library	Benchmark Name	Iterations	Total Execution Time	Average Execution Time
primitive-types	biguint_add random 1024 bits	1000000	2.020465 seconds	0.000002 seconds
primitive-types	biguint_sub random 1024 bits	1000000	1.958292 seconds	0.000002 seconds
primitive-types	biguint_divmod random 1024 bits	1000000	2.524188 seconds	0.000003 seconds
primitive-types	biguint_mul random 1024 bits	1000000	8.959132 seconds	0.000009 seconds
primitive-types	biguint_pow random 1024 bits	1000	11.547769 seconds	0.011548 seconds
primitive-types	biguint_pow_mod random 1024 bits	10	10.776888 seconds	1.077689 seconds
math	random_prime 256 bits	1	0.537939 seconds	0.537939 seconds
math	random_prime 512 bits	1	18.468756 seconds	18.468756 seconds
math	random_prime 1024 bits	1	28.295858 seconds	28.295858 seconds
math	is_prime_solovay_strassen 512 bits prime	1	3.760932 seconds	3.760932 seconds
math	is_prime_solovay_strassen 1024 bits prime	1	25.432913 seconds	25.432913 seconds
math	jacobi 512 bits prime	1	0.043537 seconds	0.043537 seconds
math	jacobi 1024 bits prime	1	0.320819 seconds	0.320819 seconds
digital-signature	rsa_key_generation 256 bits	1	0.188430 seconds	0.188430 seconds
digital-signature	rsa_key_generation 512 bits	1	1.792781 seconds	1.792781 seconds
digital-signature	rsa_key_generation 1024 bits	1	18.142116 seconds	18.142116 seconds