Remove Inf and NaN where possible

[pbiggar]

Problem: In Dark v1, it's possible to accidentally create Inf and NaN, but it was not really possible to use them.

Solution: prevent creating Inf or NaN. Any functions which (internally) create invalid floats will return Results instead:

Float::add(Float: a, Float: b) -> Result (Float, Error)
Float::subtract(Float: a, Float: b) -> Result (Float, Error)
Float::divide(Float a, Float b) -> Result (Float, Error)
Float::power(Float base, Float exponent) -> Result (Float, Error)
Float::multiply(Float: a, Float: b) -> Result (Float, Error)

[StachuDotNet]

folded into #5243