Add fiddle dependancy for Ruby 3.5

[dysonreturns]

I saw this notice while running on Ruby 3.5.0dev:
warning: fiddle used to be loaded from the standard library, but is not part of the default gems since Ruby 3.5.0

Starting Ruby 3.5.0 the gem fiddle must be added as a dependency.
This code change is backwards compatible and doesn't break numo-linalg on existing Rubies.