Split SemaphoreVerifier key points into a separate library (#875)

* refactor(scripts): added a script to convert bigint to hex

* refactor(contracts): split SemaphoreVerifier verification key points into a separate library (#330)

* chore(contracts): yarn format & lint

* refactor(contracts): update SemaphoreVerifierKeyPts library to be internal

re #330

* chore(contracts): update spacing

* chore(contracts): updated per peer review and added invariant check for VerifierKeyPts lib

* chore(contracts): update invariant check to revert with custom error

Author: jimmychu0807