Replace japicmp with revapi, restructure CI matrix, add Dependabot

- Replace japicmp-maven-plugin with revapi-maven-plugin for API
  compatibility checking against the latest released version
- Restructure CI into compile-and-check gate job followed by
  OS (ubuntu/macos/windows) x JDK (11/17/21/25) test matrix
- Add JDK 25 Error Prone profile with updated versions (2.48.0)
  and --should-stop=ifError=FLOW compiler flag
- Migrate BasicHttp2Test from deprecated SelfSignedCertificate
  to netty-pkitesting CertificateBuilder for JDK 17+ compat
- Fix flaky MultipartBasicAuthTest on Windows by reducing file
  size for 401-expecting tests to avoid socket close race
- Add Dependabot config for Maven and GitHub Actions

Author: hyperxpro

client/src/test/java/org/asynchttpclient/request/body/multipart/MultipartBasicAuthTest.java

@@ -62,7 +62,7 @@ public AbstractHandler configureHandler() throws Exception {
     }
 
     private void expectHttpResponse(Function<BoundRequestBuilder, BoundRequestBuilder> f, int expectedResponseCode) throws Throwable {
-        File file = createTempFile(1024 * 1024);
+        File file = createTempFile(1024);
 
         try (AsyncHttpClient client = asyncHttpClient()) {
             Response response = f.apply(client.preparePut(getTargetUrl()).addBodyPart(new FilePart("test", file, APPLICATION_OCTET_STREAM.toString(), UTF_8)))