Updated error message for AssertionError in shadowTuple

[jlk9]

This creates a better error message for an AssertionError in shadow tuple in jitrules.jl

@wsmoses

[github-actions]

Benchmark Results

	main	649b3f9...	main/649b3f9f6f980d...
basics/overhead	4.33 ± 0.01 ns	4.03 ± 0.01 ns	1.07
time_to_load	1.13 ± 0.012 s	1.13 ± 0.013 s	1

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).