Test fails for the samples of golang.

### What happened?

```
cd a2a-samples/samples/go
go test ./...
```

```
--- FAIL: TestSendTaskStreaming (0.00s)
client_test.go:235: expected method message/send, got message/stream
FAIL
FAIL a2a/client 0.020s
? a2a/models [no test files]
ok a2a/server (cached)
FAIL
```

### Relevant log output

```shell

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

The failing test is in a2a-samples/samples/go/a2a/client_test.go at line 235. Run 'go test ./...' from the go samples directory to reproduce. Examine the TestSendTaskStreaming function to understand the expected vs actual method values. Look at the client code that determines the method to see why 'message/stream' is being returned instead of 'message/send'.

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