Adopt strict concurrency for project

* Fix one warning related to that

Author: Alexey Ivashko

Package.swift

@@ -39,7 +39,11 @@ let package = Package(
         // Targets can depend on other targets in this package and products from dependencies.
         .target(
             name: "MCP",
-            dependencies: targetDependencies),
+            dependencies: targetDependencies,
+            swiftSettings: [
+              .enableUpcomingFeature("StrictConcurrency")
+            ]
+        ),
         .testTarget(
             name: "MCPTests",
             dependencies: ["MCP"] + targetDependencies),

Sources/MCP/Base/Messages.swift

@@ -20,7 +20,7 @@ extension Value: NotRequired {
 // MARK: -
 
 /// A method that can be used to send requests and receive responses.
-public protocol Method {
+public protocol Method: Sendable {
     /// The parameters of the method.
     associatedtype Parameters: Codable, Hashable, Sendable = Empty
     /// The result of the method.