The behavior was already accounted by filter_variable which is called directly on as a fallback by the optimizer routines

Adds condition in convert_variable_test which would fail before this change

This rewrite predated partial shape specification in SpecifyShape, and as such ignored possible shape refinement over consecutive SpecifyShapes. It now merges information across consecutive SpecifyShape. Unlike the original, preference is given to the outer SpecifyShape, similar to what local_rebroadcast_lift does.

Implement work-around for numba issue https://github.com/numba/numba/issues/8215 causing a segfault on M1 when using literal_unroll() with bools.
Closes #1023.

Resolves #816

Also avoid using `at.arange` in these tests as it always yields `ConcretizationTypeError`s in more recent versions of JAX

This "record" functionality was only used by some rather poor tests that also
needed to be removed.