🐛 Report the final URL as a redirect in native_dio_adapter - #2630

Closes #2631

cupertino_http and cronet_http follow redirects natively and expose the final URL through BaseResponseWithUrl, but ConversionLayerAdapter never passed it on. So with NativeAdapter, Response.realUri stayed the request URL and Response.redirects was always empty after a redirect.

This adds a single RedirectRecord with the final URL when it differs from the request URL. The native clients don't expose the intermediate hops or their status codes, so the record uses 302 and the request method. That's enough for realUri to be right, but redirects won't list every hop like IOHttpClientAdapter does. Happy to change the status code if you'd prefer something else.

@cfug/dio-core this touches redirect handling, so flagging it as the guidelines ask.

Added three tests to conversion_layer_adapter_test.dart: a redirected response (fails without the change), a response whose URL didn't change, and a response that doesn't report a URL. flutter test and dart analyze in plugins/native_dio_adapter pass.

Unverified: I didn't run it against a real redirect on a device.

Implementation and tests written with Claude Code; I reviewed and ran them.

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