Think more carefully about compilation of rational literals to SMTLib

Currently when we compile rational literals to SMTLib we simply cast the Rational value back to a double and then print the result. Unfortunately this obviously runs into floating point precision issues, and e.g. in andGate.vnnlib we currently end up with -3.1365920000000003 rather than -3.136592.

The right way to do this is to distinguish between rational and floating point literals in the frontend (e.g. 1.31 and 1.31f) and then make a similar distinction in SMTLib (which also supports that).

agda / agda-stdlib

Think more carefully about compilation of rational literals to SMTLib #1626