Update ScalarTensor executable

[guilara]

Proposed changes

• Add extra 3+1 quantities to compute curvature scalars.
• Disable backreaction for consistency with the test-field approximation.
• Change ScalarSource compute tag to include the coupling to curvature.
• Update evolution executable for single black hole (among these changes, including control systems).

Depends on: #6155 #6647 #6638 #6650

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Further comments

[nilsdeppe]

Not asking for a change, just a note: we've been trying to have fewer compute tags during the evolution (during observing is fine!) because the RAM/memory used by the compute tags is persistent. Instead, we've tried to move more (ideally all) of the computation that is only needed for the time derivative to that computation. This reduces the amount of persistent memory significantly and will be very important for GPUs where there's a lot less RAM for the amount of given compute.

[guilara]

Noted. Its probably not too complicated here but wouldn't do it right now because I need to work out how to move the compute tags for the full system with backreaction.