Simplify JSRemote to typed throws without 6.4 gating

Co-authored-by: Shelley <shelley@exe.dev>

Author: kateinoigakukun

Sources/JavaScriptEventLoop/JSRemote.swift

@@ -31,11 +31,10 @@ extension JSRemote where T == JSObject {
         #endif
     }
 
-    #if compiler(>=6.4)
     public func withJSObject<R: Sendable, E: Error>(
         _ body: @Sendable @escaping (JSObject) throws(E) -> R
     ) async throws(E) -> sending R {
-        #if _runtime(_multithreaded)
+        #if compiler(>=6.1) && _runtime(_multithreaded)
         if storage.sourceTid == swjs_get_worker_thread_id_cached() {
             return try body(storage.sourceObject)
         }
@@ -55,37 +54,12 @@ extension JSRemote where T == JSObject {
         return try body(storage.sourceObject)
         #endif
     }
-    #else
-    public func withJSObject<R: Sendable>(
-        _ body: @Sendable @escaping (JSObject) throws -> R
-    ) async throws -> R {
-        #if compiler(>=6.1) && _runtime(_multithreaded)
-        if storage.sourceTid == swjs_get_worker_thread_id_cached() {
-            return try body(storage.sourceObject)
-        }
-        return try await withCheckedThrowingContinuation { continuation in
-            let context = _JSRemoteContext(
-                sourceObject: storage.sourceObject,
-                body: body,
-                continuation: continuation
-            )
-            swjs_request_remote_jsobject_body(
-                storage.sourceTid,
-                Unmanaged.passRetained(context).toOpaque()
-            )
-        }
-        #else
-        return try body(storage.sourceObject)
-        #endif
-    }
-    #endif
 }
 
 @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
 private final class _JSRemoteContext: @unchecked Sendable {
     let invokeBody: () -> Bool
 
-    #if compiler(>=6.4)
     init<R: Sendable, E: Error>(
         sourceObject: JSObject,
         body: @escaping @Sendable (JSObject) throws(E) -> R,
@@ -94,30 +68,12 @@ private final class _JSRemoteContext: @unchecked Sendable {
         self.invokeBody = {
             do {
                 continuation.resume(returning: .success(try body(sourceObject)))
-                return false
-            } catch {
-                continuation.resume(returning: .failure(error as! E))
-                return true
+            } catch let error {
+                continuation.resume(returning: .failure(error))
             }
+            return false
         }
     }
-    #else
-    init<R: Sendable>(
-        sourceObject: JSObject,
-        body: @escaping @Sendable (JSObject) throws -> R,
-        continuation: CheckedContinuation<R, Error>
-    ) {
-        self.invokeBody = {
-            do {
-                continuation.resume(returning: try body(sourceObject))
-                return false
-            } catch {
-                continuation.resume(throwing: error)
-                return true
-            }
-        }
-    }
-    #endif
 }
 
 #if compiler(>=6.1)