[AltJIT] Adds AltJIT CLI tool to enable JIT on devices running iOS 17+

Commands:

altjit enable [app/pid] --udid [udid]
* Enables JIT for given app/process

altjit mount --udid [udid]
* Mounts personalized developer disk

AltJIT/Types/ALTErrorKeys.h

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+//
+//  ALTErrorKeys.h
+//  AltJIT
+//
+//  Created by Riley Testut on 9/1/23.
+//  Copyright © 2023 Riley Testut. All rights reserved.
+//
+
+@import Foundation;
+
+// Can't import AltSign (for reasons), so re-declare these constants here instead.
+extern NSErrorUserInfoKey const ALTSourceFileErrorKey;
+extern NSErrorUserInfoKey const ALTSourceLineErrorKey;
+extern NSErrorUserInfoKey const ALTAppNameErrorKey;

AltJIT/Types/ALTErrorKeys.m

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+//
+//  ALTErrorKeys.m
+//  AltJIT
+//
+//  Created by Riley Testut on 9/1/23.
+//  Copyright © 2023 Riley Testut. All rights reserved.
+//
+
+#import "ALTErrorKeys.h"
+
+NSErrorUserInfoKey const ALTSourceFileErrorKey = @"ALTSourceFile";
+NSErrorUserInfoKey const ALTSourceLineErrorKey = @"ALTSourceLine";
+NSErrorUserInfoKey const ALTAppNameErrorKey = @"appName";

AltJIT/Types/PythonCommand.swift

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+//
+//  PythonCommand.swift
+//  AltJIT
+//
+//  Created by Riley Testut on 9/6/23.
+//  Copyright © 2023 Riley Testut. All rights reserved.
+//
+
+import ArgumentParser
+
+protocol PythonCommand: AsyncParsableCommand
+{
+    var pythonPath: String? { get set }
+}
+
+extension PythonCommand
+{
+    var processEnvironment: [String: String] {
+        var environment = ProcessInfo.processInfo.environment
+        
+        if let pythonPath
+        {
+            environment["PYTHONPATH"] = pythonPath
+        }
+        
+        return environment
+    }
+    
+    mutating func prepare() async throws
+    {
+        let pythonPath = try await self.readPythonPath()
+        self.pythonPath = pythonPath.path(percentEncoded: false)
+    }
+}
+
+private extension PythonCommand
+{
+    func readPythonPath() async throws -> URL
+    {
+        let processOutput: String
+        
+        do
+        {
+            processOutput = try await Process.launchAndWait(.python3, arguments: ["-m", "site", "--user-site"])
+        }
+        catch let error as ProcessError where error.exitCode == 2
+        {
+            // Ignore exit code 2.
+            guard let output = error.output else { throw error }
+            processOutput = output
+        }
+        
+        let sanitizedOutput = processOutput.trimmingCharacters(in: .whitespacesAndNewlines)
+        
+        let pythonURL = URL(filePath: sanitizedOutput)
+        return pythonURL
+    }
+}

AltJIT/Types/RemoteServiceDiscoveryTunnel.swift

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+//
+//  RemoteServiceDiscoveryTunnel.swift
+//  AltJIT
+//
+//  Created by Riley Testut on 9/3/23.
+//  Copyright © 2023 Riley Testut. All rights reserved.
+//
+
+import Foundation
+
+final class RemoteServiceDiscoveryTunnel
+{
+    let ipAddress: String
+    let port: Int
+    
+    let process: Process
+    
+    var commandArguments: [String] {
+        ["--rsd", self.ipAddress, String(self.port)]
+    }
+    
+    init(ipAddress: String, port: Int, process: Process)
+    {
+        self.ipAddress = ipAddress
+        self.port = port
+        
+        self.process = process
+    }
+    
+    deinit
+    {
+        self.process.terminate()
+    }
+}
+
+extension RemoteServiceDiscoveryTunnel: CustomStringConvertible
+{
+    var description: String {
+        "\(self.ipAddress) \(self.port)"
+    }
+}