Move downloader and socket input parsing to xpc services (#675)

* XPC updater POC

* WIP

* obo

* WIP

* Working

* .

* .

* .

* Cleanup

* Cleanup

* Throw restrict

* Remove dead protocol.

* .

* Fix ECDSA test.

* Scripts

Sources/SecretAgent/XPCInputParser.swift

@@ -0,0 +1,23 @@
+import Foundation
+import SecretAgentKit
+import Brief
+import XPCWrappers
+
+/// Delegates all agent input parsing to an XPC service which wraps OpenSSH
+public final class XPCAgentInputParser: SSHAgentInputParserProtocol {
+
+    private let session: XPCTypedSession<SSHAgent.Request, SSHAgentInputParser.AgentParsingError>
+
+    public init() throws {
+        session = try XPCTypedSession(serviceName: "com.maxgoedjen.Secretive.AgentRequestParser", warmup: true)
+    }
+
+    public func parse(data: Data) async throws -> SSHAgent.Request {
+        try await session.send(data)
+    }
+
+    deinit {
+        session.complete()
+    }
+
+}