fix: guard HTTP_ANY undef/alias with ASYNCWEBSERVER_NO_HTTP_ANY opt-out

Co-authored-by: mathieucarbou <61346+mathieucarbou@users.noreply.github.com>

Author: Copilot

src/ESPAsyncWebServer.h

@@ -117,12 +117,17 @@ extern constexpr inline WebRequestMethodComposite operator|(WebRequestMethod l,
 // reference like AsyncWebRequestMethod::HTTP_ANY would be incorrectly expanded to AsyncWebRequestMethod::0.
 // To avoid this conflict, HTTP_ANY is provided here as a C++ constexpr (not a macro), after undefining
 // any previously defined HTTP_ANY macro. Use HTTP_ALL as the canonical non-conflicting name.
-#ifdef HTTP_ANY
-  #undef HTTP_ANY
-#endif
+// To suppress this behavior entirely (keeping any pre-existing HTTP_ANY macro and not providing the alias),
+// define ASYNCWEBSERVER_NO_HTTP_ANY before including this header.
+#if !defined(ASYNCWEBSERVER_NO_HTTP_ANY)
+  #ifdef HTTP_ANY
+    #warning "HTTP_ANY macro is already defined and will be undefined to avoid conflicts with ESPAsyncWebServer. To suppress this and keep the original macro, define ASYNCWEBSERVER_NO_HTTP_ANY and use AsyncWebRequestMethod::HTTP_ALL instead."
+    #undef HTTP_ANY
+  #endif
 namespace AsyncWebRequestMethod {
   static constexpr AsyncWebRequestMethodType HTTP_ANY = HTTP_ALL;
 }  // namespace AsyncWebRequestMethod
+#endif
 
 #if !defined(ASYNCWEBSERVER_NO_GLOBAL_HTTP_METHODS)
 // Import the method enum values to the global namespace