Mitigate runtime errors for inf values

[heinezen]

We have thought about amending the nyan language spec to mitigate runtime errors:

• If an optional(..) type member has the None value assigned, all relative operations (+=, *=, etc.) on the value will have the result None.
• The inf value for the int/float types can only be assigned -> Relative operation using inf as the operand will be disallowed.
• The special case inf *= 0 will cause a RuntimeError

From: https://matrix.to/#/!iPmyRMGnDgSMPGqgaX:matrix.org/$w2yaN1vNl21LMYIU-CMcu2nNJDGHoLr1l1OhJP-BtwI?via=matrix.org&via=sft.lol&via=stusta.de

[TheJJ]

Implemented in #87: When operating on an optional that currently is None, the member remains None.
Infinity exceptions remain.