feat(sql): follow adaptive streaming and polling responses (#4664)

SQL execution now starts with one Flight call. The server can stream
rows immediately or return a polling continuation, which the SDK follows
through the existing query handle and reader APIs. The same behavior
applies with and without parameters.

Both initial transports share direct-stream lifecycle handling. Handoffs
are explicitly negotiated; existing servers can continue returning
ordinary streams. Add coverage for streaming, deferred results,
cancellation, malformed decisions, and legacy responses.

```mermaid
flowchart TD
    A[execute_query or execute_query_async] --> B{Parameters supplied?}
    B -->|No| C[DoGet: SQL command ticket]
    B -->|Yes| D[DoExchange: SQL and Arrow parameter row]
    C --> E[Server chooses execution path]
    D --> E
    E -->|Stream| F[Initial response: streaming decision and Arrow batches]
    E -->|Defer| G[Initial response: PollInfo continuation]
    G --> H[SDK follows PollFlightInfo]
    H -->|Still running| H
    H -->|Result endpoints available| I[SDK fetches tickets with DoGet]
    F --> J[Query reader yields Arrow batches]
    I --> J
```

`execute_query` opens the reader; `execute_query_async` returns its
query handle. The caller does not select the transport or execution
path.

docs/src/python/python.md

@@ -221,10 +221,19 @@ The connected database and `default_namespace_path=["public"]` are used for
 unqualified tables. Fully qualified references can still query other databases
 and namespaces available to the same deployment. `execute_query` returns a
 reader as soon as its initial result stream is available. `execute_query_async`
-returns a query handle immediately; use it to inspect progress, open a reader,
+returns a query handle once submission is accepted; use it to inspect progress, open a reader,
 or cancel the query. The SQL client is initialized by the first query and
 retained for the lifetime of the remote connection. Query ids are random,
-connection-scoped references rather than encoded SQL or durable resume tokens:
+connection-scoped references rather than encoded SQL or durable resume tokens.
+
+Both APIs start with one Flight call. The server can stream results on that
+call or return a polling continuation that the SDK follows automatically.
+This behavior is the same with and without parameters. Open the reader directly;
+a directly streamed query needs its reader to make progress. Dropping an unread
+handle or its reader stops direct streaming. Deferred execution continues until
+explicitly cancelled.
+
+For example:
 
 ```python
 import lancedb