Clear first-party warnings from the cross-platform swift test job (#25813)

The `swift test` job added in #25344 surfaces warnings the iOS app build
hides — Xcode suppresses warnings from SPM package dependencies, and
`WordPressCore` / `WordPressCoreTests` build in Swift 6 language mode. All
three are dead code or a missing conformance, with no behavior change:

- `UserService.fetchUsers()`: dead `await` on `sequenceWithEditContext`,
  which builds a `PaginationSequence` synchronously.
- `WordPressClientFeatureTests`: three dead `try` on the non-throwing
  `WordPressClient(api:siteURL:)` initializer.
- `MockWordPressClientAPI`: five mock executors subclass wordpress-rs's
  `@unchecked Sendable` base classes without restating the conformance,
  which Swift 6 requires.

Correct for iOS too — same sources, same wordpress-rs binary, no platform
conditionals.

Author: jkmassel

Modules/Sources/WordPressCore/Users/UserService.swift

@@ -23,7 +23,7 @@ public actor UserService: UserServiceProtocol {
     }
 
     public func fetchUsers() async throws {
-        let sequence = await client.api.users.sequenceWithEditContext(params: .init(perPage: 100))
+        let sequence = client.api.users.sequenceWithEditContext(params: .init(perPage: 100))
         var started = false
         for try await users in sequence {
             if !started {

Modules/Tests/WordPressCoreTests/MockWordPressClientAPI.swift

@@ -92,7 +92,7 @@ final class MockWordPressClientAPI: WordPressClientAPI, @unchecked Sendable {
 
 // MARK: - Mock Executors
 
-final class MockApiRootRequestExecutor: ApiRootRequestExecutor {
+final class MockApiRootRequestExecutor: ApiRootRequestExecutor, @unchecked Sendable {
     private var routes: Set<String>
 
     init(routes: Set<String>) {
@@ -112,7 +112,7 @@ final class MockApiRootRequestExecutor: ApiRootRequestExecutor {
     }
 }
 
-final class MockUsersRequestExecutor: UsersRequestExecutor {
+final class MockUsersRequestExecutor: UsersRequestExecutor, @unchecked Sendable {
     override init(noHandle: UsersRequestExecutor.NoHandle) {
         super.init(noHandle: noHandle)
     }
@@ -148,7 +148,7 @@ final class MockUsersRequestExecutor: UsersRequestExecutor {
     }
 }
 
-final class MockThemesRequestExecutor: ThemesRequestExecutor {
+final class MockThemesRequestExecutor: ThemesRequestExecutor, @unchecked Sendable {
     private var isBlockTheme: Bool
 
     init(isBlockTheme: Bool) {
@@ -191,7 +191,7 @@ final class MockThemesRequestExecutor: ThemesRequestExecutor {
     }
 }
 
-final class MockSiteSettingsRequestExecutor: SiteSettingsRequestExecutor {
+final class MockSiteSettingsRequestExecutor: SiteSettingsRequestExecutor, @unchecked Sendable {
     override init(noHandle: SiteSettingsRequestExecutor.NoHandle) {
         super.init(noHandle: noHandle)
     }
@@ -235,7 +235,7 @@ final class MockSiteSettingsRequestExecutor: SiteSettingsRequestExecutor {
     }
 }
 
-final class MockWpApiDetails: WpApiDetails {
+final class MockWpApiDetails: WpApiDetails, @unchecked Sendable {
     private var routes: Set<String>
 
     init(routes: Set<String>) {

Modules/Tests/WordPressCoreTests/WordPressClientFeatureTests.swift

@@ -26,7 +26,7 @@ struct WordPressClientCachingTests {
         mockAPI.mockRoutes = ["/wp-block-editor/v1/settings"]
         mockAPI.mockIsBlockTheme = true
 
-        let client = try WordPressClient(api: mockAPI, siteURL: URL(string: "https://example.com")!)
+        let client = WordPressClient(api: mockAPI, siteURL: URL(string: "https://example.com")!)
 
         // First call - should trigger API fetches
         let result1 = try await client.supports(.blockEditorSettings)
@@ -61,7 +61,7 @@ struct WordPressClientCachingTests {
         let mockAPI = MockWordPressClientAPI()
         mockAPI.mockRoutes = ["/wp-block-editor/v1/sites/12345/settings"]
 
-        let client = try WordPressClient(api: mockAPI, siteURL: URL(string: "https://example.com")!)
+        let client = WordPressClient(api: mockAPI, siteURL: URL(string: "https://example.com")!)
 
         // Call with siteId
         let result = try await client.supports(.blockEditorSettings, forSiteId: 12345)
@@ -81,7 +81,7 @@ struct WordPressClientCachingTests {
         mockAPI.mockRoutes = ["/wp-block-editor/v1/settings", "/wp/v2/plugins"]
         mockAPI.mockIsBlockTheme = true
 
-        let client = try WordPressClient(api: mockAPI, siteURL: URL(string: "https://example.com")!)
+        let client = WordPressClient(api: mockAPI, siteURL: URL(string: "https://example.com")!)
 
         // Make multiple concurrent calls
         async let result1 = client.supports(.blockEditorSettings)