Reduce the size of Expr to 64-bytes. This works somewhat, but there are

Reduce the size of Expr to 64-bytes.  This works somewhat, but there are
test failures.  More importantly, the size reduction from 80- to 64-bytes has
not lowered the schema memory usage, but it has made the code a little bigger
and a little slower.  So the initial evidence is that this Expr refactoring
experiment is not working...

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