Simplify Scala 3 extension methods (not yet compiling)

[mpilquist]

Starting point for #10. The simplified extension methods here don't work for all hierarchy cases:

[error] -- [E007] Type Mismatch Error: /Users/mpilquist/Development/oss/twiddles/core/shared/src/test/scala/examples/Hierarchy.scala:62:33
[error] 62 |  def c: Decoder[Foo] = (int *: (string: Decoder[String]) *: bool).to[Foo]
[error]    |                                 ^^^^^^^^^^^^^^^^^^^^^^^
[error]    |                         Found:    examples.Hierarchy.Decoder[String]
[error]    |                         Required: examples.Hierarchy.Codec[A]
[error]    |
[error]    |                         where:    A is a type variable with constraint
[error]    |
[error]    | longer explanation available when compiling with `-explain`
[error] -- [E007] Type Mismatch Error: /Users/mpilquist/Development/oss/twiddles/core/shared/src/test/scala/examples/Hierarchy.scala:63:26
[error] 63 |  def d: Decoder[Foo] = ((int: Decoder[Int]) *: string *: bool).to[Foo]
[error]    |                          ^^^^^^^^^^^^^^^^^
[error]    |                         Found:    examples.Hierarchy.Decoder[Int]
[error]    |                         Required: examples.Hierarchy.Codec[A]
[error]    |
[error]    |                         where:    A is a type variable with constraint
[error]    |
[error]    | longer explanation available when compiling with `-explain`
[error] -- [E007] Type Mismatch Error: /Users/mpilquist/Development/oss/twiddles/core/shared/src/test/scala/examples/Hierarchy.scala:65:33
[error] 65 |  def f: Encoder[Foo] = (int *: (string: Encoder[String]) *: bool).to[Foo]
[error]    |                                 ^^^^^^^^^^^^^^^^^^^^^^^
[error]    |                         Found:    examples.Hierarchy.Encoder[String]
[error]    |                         Required: examples.Hierarchy.Codec[A]
[error]    |
[error]    |                         where:    A is a type variable with constraint
[error]    |
[error]    | longer explanation available when compiling with `-explain`
[error] -- [E007] Type Mismatch Error: /Users/mpilquist/Development/oss/twiddles/core/shared/src/test/scala/examples/Hierarchy.scala:66:26
[error] 66 |  def g: Encoder[Foo] = ((int: Encoder[Int]) *: string *: bool).to[Foo]
[error]    |                          ^^^^^^^^^^^^^^^^^
[error]    |                         Found:    examples.Hierarchy.Encoder[Int]
[error]    |                         Required: examples.Hierarchy.Codec[A]
[error]    |
[error]    |                         where:    A is a type variable with constraint
[error]    |
[error]    | longer explanation available when compiling with `-explain`
[error] four errors found