Add a memory knob for each one of the classic stages for which we thread the tracker through (SingleDocumentTransformationStage, MatchStage, LookUpStage, RedactStage). This knob will be used to bound the memory usage of the expressions, as a safeguard, until the per-query limit is set.

One per-stage limit covers all expressions uniformly, replaces N per-expression knobs, reuses the existing assertWithinMemoryLimit path (no per-expression code), and is always-on with a finite default, independent of the per-query limit. The default is 100MB, the standard default for our other memory limits, including the existing per-expression ones.