Allow fixing of scaling model corrections

[jbeilstenedmands]

Certain workflows would benefit from being able to fix particular scaling model corrections.

The use case in mind is to refine an absorption correction when scaling multiple sweeps from a crystal, then in subsequent scaling jobs when combining with other crystals, to be able to keep the individual absorption corrections without further refinement.
Or perhaps if one could determine an absorption correction empirically, then this can be fixed during scaling model minimisation.

Achieved with a phil parameter with the syntax model.correction.fix=correction_name e.g. physical.correction.fix=absorption.

[codecov]

Codecov Report

Merging #1883 (950265a) into main (e7d1423) will increase coverage by 0.02%.
The diff coverage is 84.78%.

❗ Current head 950265a differs from pull request most recent head 2152c6a. Consider uploading reports for the commit 2152c6a to get more accurate results

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