Bad numbers in test_airy.cpp

Look at test_airy.cpp
test_airy.cpp - compiles and runs but the numbers are wierd but the tests maybe bogus anyway.
Maybe repurpose this.
Lots of unused variables. Fixed.

Rename to debug_airy.cpp?

Start by reading test_airy.cpp and running its existing tests to inspect the unexpected numerical results and whether the assertions are meaningful. Determine whether the file should be repaired or repurposed, remove any remaining unused variables, and confirm the chosen name and test behavior are clear.

Written by the indexing model from the issue text.