Harden PTT audio and the 1.7.1 release (#1423)

Centralize PTT and voice audio-session ownership, harden courier/bridge/outbox delivery and recovery, correct location and delivery-state races, add privacy/release metadata, and ship reproducible universal Arti slices with Release CI coverage.

Validated by the full iOS suite, repeated audio/fragment/performance regressions, BitFoundation tests, strict lint and dead-code analysis, universal iOS Release builds, and iOS/macOS archives.

localPackages/BitFoundation/Tests/BitFoundationTests/MockKeychain.swift

@@ -9,7 +9,7 @@
 import Foundation
 import BitFoundation
 
-// TODO: Create a module for test helpers
+// Kept local until the test-helper module is split out.
 final class MockKeychain: KeychainManagerProtocol {
     private var storage: [String: Data] = [:]
     private var serviceStorage: [String: [String: Data]] = [:]

localPackages/BitFoundation/Tests/BitFoundationTests/TestConstants.swift

@@ -8,7 +8,7 @@
 
 import Foundation
 
-// TODO: Create a module for test helpers
+// Kept local until the test-helper module is split out.
 struct TestConstants {
     static let defaultTimeout: TimeInterval = 5.0
     static let shortTimeout: TimeInterval = 1.0

localPackages/BitFoundation/Tests/BitFoundationTests/TestHelpers.swift

@@ -10,7 +10,7 @@ import Foundation
 import CryptoKit
 @testable import BitFoundation
 
-// TODO: Create a module for test helpers
+// Kept local until the test-helper module is split out.
 final class TestHelpers {
     
     // MARK: - Key Generation