Drop Swift 5.10 (#46)

### Motivation:

Swift 5.10 is no longer supported, we should bump the swift-tools
version.

### Modifications:

* Update Swift tools version to 6.0

### Result:

Code reflects our support window.

Author: yigityazicilar

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.10
+// swift-tools-version:6.0
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the SwiftNIO open source project
@@ -19,10 +19,6 @@ let strictConcurrencyDevelopment = false
 
 let strictConcurrencySettings: [SwiftSetting] = {
     var initialSettings: [SwiftSetting] = []
-    initialSettings.append(contentsOf: [
-        .enableUpcomingFeature("StrictConcurrency"),
-        .enableUpcomingFeature("InferSendableFromCaptures"),
-    ])
 
     if strictConcurrencyDevelopment {
         // -warnings-as-errors here is a workaround so that IDE-based development can
@@ -88,7 +84,8 @@ let package = Package(
             name: "ObliviousXHelpers",
             dependencies: [
                 .product(name: "Crypto", package: "swift-crypto")
-            ]
+            ],
+            swiftSettings: strictConcurrencySettings
         ),
         .testTarget(
             name: "ObliviousHTTPTests",

Sources/ObliviousDoH/ODoHRoutine.swift

@@ -89,7 +89,7 @@ public enum ODoH: Sendable {
     ///
     /// Contains common functionality for both client and server ODoH operations.
     /// Initialized with a configuration containing the target's public key and algorithm parameters.
-    internal struct RoutineCore {
+    internal struct RoutineCore: Sendable {
         internal var ct: HPKE.Ciphersuite
         internal var pkR: any HPKEDiffieHellmanPublicKey
         internal var keyID: Data
@@ -178,7 +178,7 @@ public enum ODoH: Sendable {
     ///
     /// Handles the client-side cryptographic operations for Oblivious DNS over HTTPS.
     /// Initialized with a configuration containing the target's public key and algorithm parameters.
-    public struct ClientRoutine {
+    public struct ClientRoutine: Sendable {
         private var core: RoutineCore
 
         /// Initialize ODoH client routine with target server configuration.
@@ -345,7 +345,7 @@ public enum ODoH: Sendable {
     ///
     /// Handles the server-side cryptographic operations for Oblivious DNS over HTTPS.
     /// Initialized with a configuration containing the server's public key and algorithm parameters.
-    public struct ServerRoutine {
+    public struct ServerRoutine: Sendable {
         private var core: RoutineCore
 
         /// Initialize ODoH server routine with server configuration.