Use HTTPFields.contains

Doesn't construct http field contents

Sources/Hummingbird/Middleware/CORSMiddleware.swift

@@ -86,7 +86,7 @@ public struct CORSMiddleware<Context: BaseRequestContext>: RouterMiddleware {
     /// apply CORS middleware
     public func handle(_ request: Request, context: Context, next: (Request, Context) async throws -> Response) async throws -> Response {
         // if no origin header then don't apply CORS
-        guard request.headers[.origin] != nil else {
+        guard request.headers.contains(.origin) else {
             return try await next(request, context)
         }
 

Sources/Hummingbird/Router/ResponseGenerator.swift

@@ -119,7 +119,7 @@ public struct EditedResponse<Generator: ResponseGenerator>: ResponseGenerator {
             // only add headers from generated response if they don't exist in override headers
             var headers = self.headers
             for header in response.headers {
-                if headers[header.name] == nil {
+                if !headers.contains(header.name) {
                     headers.append(header)
                 }
             }

Sources/HummingbirdCore/Response/Response.swift

@@ -28,7 +28,7 @@ public struct Response: Sendable {
     public init(status: HTTPResponse.Status, headers: HTTPFields = .init(), body: ResponseBody = .init()) {
         self.head = .init(status: status, headerFields: headers)
         self.body = body
-        if let contentLength = body.contentLength, headers[values: .contentLength].count == 0 {
+        if let contentLength = body.contentLength, !headers.contains(.contentLength) {
             self.head.headerFields[.contentLength] = String(describing: contentLength)
         }
     }