Introduce request#isMethod(...) to check the http method of the request (fixes #398)

[mathieucarbou]

Fixes #398

Note: this PR does not fix the definition in arduino-pico.

Instead, it provides a new way to check for a request method, and this way is implemented differently in PICO.

If users are still reegistering their handler in PICO with | like that

webServer.on("/ping", HTTP_GET | HTTP_POST, [](AsyncWebServerRequest* request) {
  request->send(200, "text/plain", "pong");
});

then of course it won't solve anything.

[Copilot]

Pull request overview

This PR introduces AsyncWebServerRequest::isMethod(...) to provide correct HTTP method matching across platforms, specifically addressing RP2040/RP2350 where request methods are not a bitmask and &-based checks produce false positives (issue #398).

Changes:

• Added AsyncWebServerRequest::isMethod(WebRequestMethodComposite) with RP2040/RP2350-specific semantics (equality / HTTP_ANY).
• Updated handler method checks to use request->isMethod(...) instead of bitwise &.
• Updated methodToString() to use isMethod(...) for method name resolution.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/ESPAsyncWebServer.h	Adds AsyncWebServerRequest::isMethod(...) with RP2040/RP2350-specific handling.
src/WebHandlers.cpp	Switches handler method filtering to request->isMethod(_method) to avoid RP false positives.
src/WebRequest.cpp	Updates methodToString() to rely on isMethod(...) instead of & checks.
src/AsyncJson.cpp	Changes JSON handler method filtering logic (but currently introduces a behavior regression by ignoring _method).

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[mathieucarbou]

Closing in favor of #400