performance: expression calculations are hydrated 3 times

Hydrating expressions is relatively expensive: .5ms is typical in a real app for a first_name <> last_name (although using flame on, so it's probably slowed down by the instrumentation)

There may be opportunities to improve performance of the hydration, but it appears that there are circumstances where the hydration occurs 3 times in a load so if it can be done once, that would improve performance:

Top level:

Zoom in on first two examples:

Zoom in on third example:

No files, tests, or entry points are named. Start by reproducing a load involving a first_name <> last_name expression with flame instrumentation, then trace where expression hydration occurs. Done means confirming hydration happens once per load without changing the resulting expression values, and measuring the performance difference.

Written by the indexing model from the issue text.