36018 system tests for multi ws focus

[andy-bridger]

Description of work

Added System Test for focussing of Polaris and GEM, checking that when multiple ws are passed they are dealt with correctly by input_mode = "Individual"/"Summed"

Additionally reformatted code to avoid repetition

Summary of work

Tests now exist which take run_number="xxxxx,yyyyy" rather than previously where all tests only ever operated on a single run workspace.

The tests simply check for the correct output workspaces i.e. for "Individual" : xxxxx.gsas, xxxxx.nxs, yyyyy.gsas, and yyyyy.nxs should all be produced. For "Summed" only xxxxx,yyyyy.gsas and xxxxx,yyyyy.nxs should be produced.

Fixes #36018.

Further detail of work

Refactoring of code chosen to do Multiple class inheritance but leave the Base Class without comprehensive implementation. Bogging it down with abstractmethod decorators for the not yet instantiated assert methods that need to be inherited from the Testing Class was deemed to be unnecessary for code that is not user-facing.

To test:

Run ISIS_PowderPolarisTest.py and ISIS_PowderGemTest.py

This does not require release notes because no change to any user-facing code

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[sf1919]

Please can you change the branch to main? Only v6.12 milestone bug fixes should be on release-next.

[andy-bridger]

Whoops, I actually had a bit of a faff moving this branch from main to release-next, but fortunately I have the original branch based off main. If you are happy I will just close this PR and reopen the other branch?