Allow for using explicit copy methods in classes

[KacperFKorban]

fixes part of #234

[adamw]

Thanks :)

[adamw]

@KacperFKorban I'm getting the following error in tapir after updating:

[error] -- Error: /Users/adamw/projects/tapir/docs/openapi-docs/src/test/scalajvm/sttp/tapir/docs/openapi/VerifyYamlTest.scala:847:15
[error] 847 |    docs.modify(_.paths.pathItems)
[error]     |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[error]     |Unsupported source object: must be a case class or sealed trait, but got: val <none>

Followed by a compiler crash:

[error] ## Exception when compiling 20 sources to /Users/adamw/projects/tapir/docs/openapi-docs/target/jvm-3/test-classes
[error] java.lang.AssertionError: assertion failed
[error] scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:11)
[error] dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:2439)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3026)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3114)
[error] dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:153)
[error] dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:915)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3187)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3191)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3213)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3259)
[error] dotty.tools.dotc.typer.Typer.typedBlockStats(Typer.scala:1161)
[error] dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:1165)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3058)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3115)
[error] dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:153)
[error] dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:915)
(...)

The definition of .pathItems doesn't look extraordinary:

final case class Paths(
    pathItems: ListMap[String, PathItem] = ListMap.empty,
    extensions: ListMap[String, ExtensionValue] = ListMap.empty
)

Do you maybe have any ideas what could be the cause?

[KacperFKorban]

@adamw I'll take a look. quicklens uses named accessors now instead of the copy$default methods, so there might be a bug in there.