[Chore] Clean-up Buildable ExecutorOp implementation

Context: got distracted by this while working on !1351 (merged), but by the time I was finishing up, that MR already was reviewed, so I've opted to split this off.

Description

Problem: Buildable ExecutorOp instance includes not only the logic for ExecutorOp, but also for *Operation. This seems wrong from the separation of concerns standpoint, plus it's harder to test.

Solution: Add Buildable instances for individual *Operation types, add doctests, tweak the instances to produce good results. Make Buildable ExecutorOp delegate to these instances.

This also adds quoteF to Fmt for minor convenience.

Related issue(s)

Resolves None

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