fix: Scala 3.8 syntax compat fixes and import cleanup

[He-Pin]

Motivation

Scala 3.8 introduces stricter syntax requirements and new warnings for patterns that will be removed in future versions. Several code patterns need updates for forward compatibility.

Modification

• Replace _ wildcard type with ? in scala-3 source directories (Platform.scala, ClusterReceptionistProtocol.scala)
• Add explicit using keyword for implicit argument forwarding in ByteIterator.scala (scala-3): getShort(using byteOrder)
• Add @unchecked annotations for type-test patterns that cannot be checked at runtime in AskPattern.scala and ByteString.scala
• Replace eta expansion syntax apply _ with explicit lambda ref => apply(ref) in Patterns.scala (4 occurrences)
• Fix SortedSet.empty implicit ordering in SimpleDnsCache.scala by binding ordering as implicit val before calling .empty
• Replace infix type syntax AnyRef JPair AnyRef with JPair[AnyRef, AnyRef] in ConstantFun.scala
• Add LogSource implicit val bindings for Logging calls in Ops.scala
• Add implicit def selfSender in SourceRefImpl.scala
• Fix Logging factory call in MultiNodeSpec.scala
• Fix discard result pattern in FixedBufferSpec.scala
• Import reordering and formatting across ~35 files for scalafmt compliance
• Fix Scaladoc apostrophe in CallingThreadDispatcher.scala
• Fix doc reference "Java 8" to "Java" in operators/index.md
• Remove unused import in SnapshotStorage.scala

Result

Code compiles cleanly with Scala 3.8 syntax requirements. No behavioral changes to the runtime.

Tests

• Not run - syntax compat fixes, verified by cross-compilation

References

None - proactive Scala 3.8 forward compatibility

[pjfanning]

lgtm