Fix protected access

[gtrevisan]

fix:

• W0212 @ https://pylint.pycqa.org/en/latest/user_guide/messages/warning/protected-access.html

close:

• Fix access or scope of private-member methods #296

by:

• removing leading underscore from _cached_results in core/physics_method/caching.py,
• temporarily disabling the warning for two specific calls to _get_ip_parameters from settings/domain_setting.py.
• flipping the convention of all physics methods in terms of the with/without underscore naming convention.

[amdecker]

Flipped the underscore/no underscore physics method