fix: Opt-in to RFC 7578 multipart field formatting

This is a new feature from Speakeasy that supports RFC 7578-compliant format (instead of the `fieldname.[]` style).

Author: rwjblue-glean

.speakeasy/gen.yaml

@@ -62,7 +62,7 @@ java:
     shortName: MIT
     url: https://mit-license.org/
   maxMethodParams: 4
-  multipartArrayFormat: legacy
+  multipartArrayFormat: standard
   nullFriendlyParameters: false
   openUnions: true
   operationScopedParams: true