fix: handle unexpected tokens when parsing stabs

[doorgan]

Fix #75

The issue was that stab_state was leaking into inner stabs, corrupting the parser state and causing the wrong tokens to be handed to parse_stab_expression. Resetting the state seems to fix this. The other solution I found was to add a fallback clause to parse_stab_expression but that felt too hacky because we were still dealing with corrupt parser state.

Also adds a bunch of tests for stabs to make sure the stab_state logic is not breaking anything else

[doorgan]

I think this also fixed #74 because the traces hit the same clause, but I'm still trying to come up with a reproduction case to confirm

[doorgan]

It partially fixed #74, I found that this:

Spitfire.parse("a -> b -> fn} -> c")

Used to crash with the error reported in that issue, and after this fix it now returns {:error, :no_fuel_remaining}, so it's not completely fixed. I'll update that issue and work on a separate fix