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GH-44363: [C#] Handle Flight data with zero batches (#45315)

### Rationale for this change

See #44363. This improves compatibility with other Flight implementations and means user code works with empty data without needing to treat it as a special case to work around this limitation.

### What changes are included in this PR?

* Adds new async overloads of `FlightClient.StartPut` that immediately send the schema, before any data batches are sent.
* Updates the test server to send the schema on `DoGet` even when there are no data batches.
* Enables the `primitive_no_batches` test case for C# Flight.

### Are these changes tested?

Yes, using a new unit test and with the integration tests.

### Are there any user-facing changes?

Yes. New overloads of the `FlightClient.StartPut` method have been added that are async and accept a `Schema` parameter, and ensure the schema is sent when no data batches are sent.

* GitHub Issue: #44363

Authored-by: Adam Reeve <adreeve@gmail.com>
Signed-off-by: Curt Hagenlocher <curt@hagenlocher.org>