fix: resolve Swift 6 warnings - shadowing generics

**Motivation:**

Currently, project contains quite amount of shadowed generics warnings.
All this warnings will become errors with Swift 6.

**Modifications:**

Each warning occurency is updated to use slightly different type
parameters name.

**Result:**

- Partially addresses apple#1125

Sources/DistributedActorsTestKit/TestProbes.swift

@@ -696,7 +696,7 @@ extension ActorTestProbe {
     /// Without this it may happen that we asked the probe to watch an actor, and send a message to the actor directly,
     /// and our direct message arrives first, before the watch at the destination, causing potentially confusing behavior
     /// in some very ordering delicate testing scenarios.
-    public func forward<Message>(_ message: Message, to target: _ActorRef<Message>, file: String = #filePath, line: UInt = #line) where Message: Codable {
+    public func forward<M>(_ message: M, to target: _ActorRef<M>, file: String = #filePath, line: UInt = #line) where M: Codable {
         self.internalRef.tell(ProbeCommands.forwardCommand(send: { () in target.tell(message, file: file, line: line) }))
     }
 

Sources/DistributedCluster/Adapters.swift

@@ -384,15 +384,15 @@ extension SubReceiveAdapter {
         return c.result
     }
 
-    func _resolve<Message>(context: _ResolveContext<Message>) -> _ActorRef<Message> {
+    func _resolve<M>(context: _ResolveContext<M>) -> _ActorRef<M> {
         guard context.selectorSegments.first == nil,
               self.id.incarnation == context.id.incarnation
         else {
             return context.personalDeadLetters
         }
 
         switch self.myself {
-        case let myself as _ActorRef<Message>:
+        case let myself as _ActorRef<M>:
             return myself
         default:
             return context.personalDeadLetters

Sources/DistributedCluster/Collections/_LinkedBlockingQueue.swift

@@ -17,14 +17,14 @@ import NIO
 /// Not intended for general use.
 public final class _LinkedBlockingQueue<A>: @unchecked Sendable {
     @usableFromInline
-    final class Node<A>: @unchecked Sendable {
+    final class Node<T>: @unchecked Sendable {
         @usableFromInline
-        var item: A?
+        var item: T?
         @usableFromInline
-        var next: Node<A>?
+        var next: Node<T>?
 
         @usableFromInline
-        init(_ item: A?) {
+        init(_ item: T?) {
             self.item = item
         }
     }

Sources/DistributedCluster/_ActorShell.swift

@@ -626,19 +626,19 @@ public final class _ActorShell<Message: Codable>: _ActorContext<Message>, Abstra
     }
 
     @discardableResult
-    override public func _spawnWatch<Message>(
+    override public func _spawnWatch<M>(
         _ naming: _ActorNaming,
-        of type: Message.Type = Message.self,
+        of type: M.Type = M.self,
         props: _Props = _Props(),
         file: String = #filePath, line: UInt = #line,
-        _ behavior: _Behavior<Message>
-    ) throws -> _ActorRef<Message>
-        where Message: Codable
+        _ behavior: _Behavior<M>
+    ) throws -> _ActorRef<M>
+        where M: Codable
     {
         self.watch(try self._spawn(naming, props: props, behavior))
     }
 
-    override public func stop<Message: Codable>(child ref: _ActorRef<Message>) throws {
+    override public func stop<M: Codable>(child ref: _ActorRef<M>) throws {
         try self._stop(child: ref)
     }