Replace secp_utils usage of big.Int with uint256 library.

[rodrigo-pino]

In ./pkg/hintrunner/utils/secp_utils.go there are utilities for elliptic curves. They used big.Int unnecessarily because all values are smaller than 2**256 - 1.

The task is to replace all use of big.Int with uint256 which is waaaaaaay faster.

[TAdev0]

Hi @rodrigo-pino may i be assigned to this issue? thanks!

[rodrigo-pino]

Hi @TAdev0 is yours. This are the things you need to do:

1. Swap the arithmetic that uses big.Int for uint256.
2. Output should be actual values and not references to them. (a.k.a. uint256 instead of *uint256)
3. The functions getBaseBig & getSecPBig should return a constant and not perform any operation. Currently, they are: (i) creating a big int and (ii) setting it up using a string. They should return a uint256 without any of these operations. Also, it makes no sense they return a boolean as a second output.

Tell me if you need help with anything!

[rodrigo-pino]

We are using github.com/holiman/uint256 as our uint256 library which is already part of the VM packages

[TAdev0]

Thanks a lot for explanations, will be useful as this is my first Go contribution :)