[BUG] Fixing typing in helpers function

[jamesETsmith]

Summary

This PR fixes a typo in the helpers (calcutate --> calculate) and adds the helpers to the docs and adds tests for the python wrappers of the helpers.

Details

• Fixes typo https://github.com/qognitive/fast-pauli/blob/f9e94d0b0e354a5593683b533e5829e9c2036e63/fast_pauli/cpp/src/fast_pauli.cpp#L1139
• Adds helpers C++ and Python API to the docs
• Adds Python tests for the Python interface of the helpers
• Cleans up the C++ docstrings
• Adding Python docstrings for the helpers

Related Issues

• Fixes #85