perf(context): add fast path to c.json() matching c.text() optimization (#4707)

* perf: add fast path to c.json() matching c.text() optimization

Skip #newResponse() and Headers allocation when no status, headers,
or finalized state exists. Creates Response directly with inline
Content-Type header, matching the existing c.text() fast path pattern.

* ci: apply automated fixes

* use `Response.json()`

* don't use `any`

* refactor with `useFastPath`

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Yusuke Wada <yusuke@kamawada.com>

Author: 3 people

src/context.ts

@@ -657,6 +657,10 @@ export class Context<
     headers?: HeaderRecord
   ): ReturnType<BodyRespond> => this.#newResponse(data, arg, headers) as ReturnType<BodyRespond>
 
+  #useFastPath(): boolean {
+    return !this.#preparedHeaders && !this.#status && !this.finalized
+  }
+
   /**
    * `.text()` can render text as `Content-Type:text/plain`.
    *
@@ -674,7 +678,7 @@ export class Context<
     arg?: ContentfulStatusCode | ResponseOrInit,
     headers?: HeaderRecord
   ): ReturnType<TextRespond> => {
-    return !this.#preparedHeaders && !this.#status && !arg && !headers && !this.finalized
+    return this.#useFastPath() && !arg && !headers
       ? (new Response(text) as ReturnType<TextRespond>)
       : (this.#newResponse(
           text,
@@ -703,11 +707,15 @@ export class Context<
     arg?: U | ResponseOrInit<U>,
     headers?: HeaderRecord
   ): JSONRespondReturn<T, U> => {
-    return this.#newResponse(
-      JSON.stringify(object),
-      arg,
-      setDefaultContentType('application/json', headers)
-    ) /* eslint-disable @typescript-eslint/no-explicit-any */ as any
+    return (
+      this.#useFastPath() && !arg && !headers
+        ? Response.json(object)
+        : this.#newResponse(
+            JSON.stringify(object),
+            arg,
+            setDefaultContentType('application/json', headers)
+          )
+    ) as JSONRespondReturn<T, U>
   }
 
   html: HTMLRespond = (