Usage of implicit method attributeKey defined in object JavaMapping, which is not accessible here

## Steps

### build.sbt

```scala
scalaVersion := "3.8.4"

val pekkoVersion = "2.0.0-M3"

libraryDependencies ++= Seq(
"org.apache.pekko" %% "pekko-actor-typed" % pekkoVersion,
"org.apache.pekko" %% "pekko-stream" % pekkoVersion,
"org.apache.pekko" %% "pekko-http" % "2.0.0-M1"
)

scalacOptions += "-deprecation"
```

### project/build.properties

```properties
sbt.version=1.12.11
```

### A.scala

```scala
import org.apache.pekko.http.scaladsl.model.HttpRequest
import org.apache.pekko.http.scaladsl.model.AttributeKeys

class A {
def b(request: HttpRequest) = request.attribute(AttributeKeys.remoteAddress)
}
```

## Problem

```
[warn] 5 | def b(request: HttpRequest) = request.attribute(AttributeKeys.remoteAddress)
[warn] | ^
[warn] |Usage of implicit method attributeKey defined in object JavaMapping, which is not accessible here. In Scala 3.10, this implicit will no longer be found.
```

## Note

- https://github.com/scala/scala3/pull/25608
- https://github.com/scala/scala3/pull/25516

Reproduce the warning with the build.sbt, project/build.properties, and A.scala example, starting at AttributeKeys.remoteAddress and request.attribute. Trace the implicit attributeKey lookup and the JavaMapping visibility involved, using the linked Scala 3 changes for context. Done means the example compiles without this deprecation warning under the stated Scala version.

Written by the indexing model from the issue text.