fix: generalize DivisionRing.toOfScientific (#9947)

If you can cast a rat to a type, then we probably want decimal notation to work there too.

This has the benefit of making the instance computable even in cases where some parts of the division ring structure are not.
It also means that this could apply to matrices of rational numbers, which are not a division ring, but could have a rat cast.

Mathlib/Algebra/Field/Defs.lean

@@ -159,7 +159,7 @@ end DivisionRing
 
 section OfScientific
 
-instance DivisionRing.toOfScientific [DivisionRing K] : OfScientific K where
+instance RatCast.toOfScientific [RatCast K] : OfScientific K where
   ofScientific (m : ℕ) (b : Bool) (d : ℕ) := Rat.ofScientific m b d
 
 end OfScientific