Rename repository to bignum

[Savio-Sou]

Problem

Noir does not support hyphens in crate names, hence using underscores for naming shall be avoided as a general best practice.

Happy Case

Rename this repository from noir-bignum to bignum.

Alternatives considered

Renaming to noir_bignum is also an option. To discuss if we prefer promoting the use of noir_ prefix for all Noir libraries or not.

Would you like to submit a PR for this Issue?

No