Fix Linux build and address remaining warnings

Author: gwynne

Sources/StructuredAPIClient/Handlers/TokenAuthenticationHandler.swift

@@ -13,7 +13,7 @@
 
 import Foundation
 #if canImport(FoundationNetworking)
-import FoundationNetworking
+@preconcurrency import FoundationNetworking
 #endif
 import Logging
 

Sources/StructuredAPIClient/NetworkClient.swift

@@ -13,7 +13,7 @@
 
 import Foundation
 #if canImport(FoundationNetworking)
-import FoundationNetworking
+@preconcurrency import FoundationNetworking
 #endif
 import Logging
 
@@ -60,3 +60,13 @@ internal extension DispatchTime {
         Double(self.uptimeNanoseconds) / 1_000_000
     }
 }
+
+#if !canImport(Darwin)
+extension NSLocking {
+    package func withLock<R>(_ body: @Sendable () throws -> R) rethrows -> R {
+        self.lock()
+        defer { self.unlock() }
+        return try body()
+    }
+}
+#endif

Sources/StructuredAPIClient/Transport/TransportFailure.swift

@@ -11,6 +11,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if !canImport(Darwin)
+@preconcurrency
+#endif
 import Foundation
 #if canImport(FoundationNetworking)
 import FoundationNetworking

Sources/StructuredAPIClient/Transport/URLSessionTransport+AsyncAwait.swift

@@ -16,6 +16,8 @@ import Foundation
 import FoundationNetworking
 #endif
 
+#if canImport(Darwin)
+
 @available(macOS 12.0, iOS 15.0, watchOS 8.0, tvOS 15.0, *)
 extension URLSessionTransport {
 
@@ -38,3 +40,5 @@ extension URLSessionTransport {
         }
     }
 }
+
+#endif

Sources/StructuredAPIClient/Transport/URLSessionTransport.swift

@@ -13,7 +13,7 @@
 
 import Foundation
 #if canImport(FoundationNetworking)
-import FoundationNetworking
+@preconcurrency import FoundationNetworking
 #endif
 import HTTPTypes
 

Sources/StructuredAPIClientTestSupport/TestTransport.swift

@@ -13,7 +13,7 @@
 
 import Foundation
 #if canImport(FoundationNetworking)
-import FoundationNetworking
+@preconcurrency import FoundationNetworking
 #endif
 import StructuredAPIClient