Some fixes for Scala 3 mock-method metadata

[jozic]

I was testing these on real projects and figured out some issues for Scala 3 mock-method metadata implementation: overloaded methods conflict, storing primitives in value classes cache. Also added some docs explaining how mock method should be wrapped (if needed) in Scala 3

More details

1. Overload dedup by symbol, not fullName.
   In Scala 3, all overloads of a method share the same Symbol.fullName. The old mutable.Set[String] dedup kept only the first overload encountered, silently dropping e.g. a vararg overload that shared a name with plain overloads. Changed to mutable.Set[Symbol] — each overload is a distinct symbol, so all survive.

2. isPrimitiveType guard in returnsValueClassFor.
   Int <:< AnyVal is true at Scala's type level, so without an explicit check, returnsValueClassFor(TypeRepr.of[Int]) would return true and primitive-returning methods would be wrongly stored as value-class returns. The guard prevents false positives.

3. Only true entries go into the returnsValueClass cache.
   The old code stored (method, false) for every method; the new code stores only true entries. getReturnsValueClass returning None is the same signal as false — the cache can be smaller and the intent is clearer.

4. ReflectionUtils.returnsValueClass — remove broken fallback
   The old fallback classOf[AnyVal].isAssignableFrom(returnType) compiled to classOf[Object].isAssignableFrom(returnType) in Scala 3, returning true for every reference type. With only-true cache entries this fallback is also unnecessary — getOrElse(false) is correct and safe.

5. MockCreator scaladoc + note in README — inline wrapper requirement explained

plus new tests to verify the fixes

[jozic]

@TimvdLippe please check this out. Thanks!

[TimvdLippe]

Nice comments! Despite my minimal Scala knowledge, I was able to understand why these fixes were required.