Scala 2 "implicit" no longer supported with -source:future on Scala 3.7.3

[LeifW]

Scala 3.7.3 includes an item in its release notes:

Disallow Scala 2 implicits under -source:future scala/scala3#23472

E.g. the following Smithy definition:

use alloy#openEnum

union UnionA {
  stringValue: String
  intValue: Integer
}

@openEnum
enum EnumA {
  VALUE_1
}

Generates code with schema values declared using Scala 2 implicit syntax:

implicit val schema: Schema[EnumA] = enumeration(tag, values).withId(id).addHints(hints)

 implicit val schema: Schema[UnionA] = union(
    UnionA.StringValueCase.alt,
    UnionA.IntValueCase.alt,
  )

Which the compiler now rejects with: "implicit vals are no longer supported, use a given clause instead."

Another Scala 3 codegen nit: the generated smithy4s.Endpoint has a series of _ for the type param positions, which has been getting a deprecation warning for a while now: "_ is deprecated for wildcard arguments of types: use ? instead"