Summary

• Increase warnings stacklevel to 2, to point to the caller instead of warnings.warn
• Un-ignore RUFF B028: Checks for warnings.warn calls without an explicit stacklevel keyword argument
• Replace explicit stacklevel=1, people might have misunderstood this. It's not "default stacklevel" that is bad, but "default stacklevel as 1" that is not informative
• Remove unnecessary explicit UserWarning as it's default:

  The category argument, if given, must be a warning category class; it defaults to UserWarning.

• Change _MPResterLegacy from default UserWarning to FutureWarning

  pymatgen/src/pymatgen/ext/matproj_legacy.py

  Line 169 in 31f1e1f

  "You are using the legacy MPRester. This version of the MPRester will no longer be updated. "

Example

Stacklevel 1:

UserWarning: Non-default endpoint used:xxxx
warnings.warn(f"Non-default endpoint used: {self.preamble}", stacklevel=1)

vs

Stacklevel 2:

UserWarning: Non-default endpoint used: xxxx
  mpr = _MPResterLegacy(MP_API_KEY)