Add secp256k1 Module with Field and Group Classes to Testing Framework

This PR redefines the cryptographic primitives used in the Bitcoin core's functional testing framework. And adds a new module in the python framework as secp256k1.py. This module includes all the cryptographic primitives. So the way to review this PR is to understand some fun basic crypto maths. For more details, visit the PR discussion page: https://github.com/Bitshala/Bitcoin-PR-Review-Club/discussions/32 Review Club Joining instruction: https://github.com/Bitshala/Bitcoin-PR-Review-Club Website: https://www.bitshala.org/ Community: https://discord.gg/atjEPVTdsQ