[TASK-263] Remove async from queueing while writing

[fresh-borzoni]

Summary

closes #263

• Make write queueing synchronous by replacing tokio::sync::Mutex with parking_lot::Mutex in the core accumulator and writer client
• upsert(), delete(), append() now queue writes synchronously (no await needed) and return a WriteResultHandle
• WriteResultHandle supports both fire-and-forget (ignore the handle) and per-record ack (await handle.wait())
• flush() remains async (real network I/O)
• Apply same pattern to Python and C++ bindings

[fresh-borzoni]

@luoyuxia @leekeiabstraction
Apreciate review here, PTAL 🙏

[Copilot]

Pull request overview

This PR removes unnecessary async from the write queueing path by switching internal queue synchronization to parking_lot::Mutex, making upsert(), delete(), and append() queue synchronously while still allowing async acknowledgement via a returned handle/future; async behavior is retained for flush() since it performs network I/O.

Changes:

• Replace async queueing (tokio::sync::Mutex) with synchronous locking (parking_lot::Mutex) in the core write accumulator and writer client.
• Update Rust API call sites (tests/examples/docs) to remove the first await on queueing methods while keeping per-record ack via awaiting the returned handle.
• Apply the same synchronous-queue + async-ack pattern to Python and C++ bindings (including a new Python WriteResultHandle).

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
crates/fluss/src/client/write/accumulator.rs	Switch queue locks to parking_lot::Mutex and make queue operations synchronous (append/ready/drain/re_enqueue).
crates/fluss/src/client/write/writer_client.rs	Make send() synchronous and remove awaits on accumulation.
crates/fluss/src/client/write/sender.rs	Adjust sender to use synchronous accumulator APIs; keep async for network/metadata updates.
crates/fluss/src/client/write/mod.rs	Update docs for new call pattern around WriteResultFuture.
crates/fluss/src/client/table/append.rs	Make append/append_arrow_batch synchronous queueing returning WriteResultFuture.
crates/fluss/src/client/table/upsert.rs	Make upsert/delete synchronous queueing returning WriteResultFuture.
crates/fluss/tests/integration/log_table.rs	Remove await from queueing calls to match the new synchronous API.
crates/fluss/tests/integration/kv_table.rs	Remove await from queueing calls and keep per-record ack via awaiting the returned handle.
crates/examples/src/example_table.rs	Update example to use synchronous queueing + async flush.
crates/examples/src/example_kv_table.rs	Update KV example for synchronous queueing + optional per-record ack.
crates/examples/src/example_partitioned_kv_table.rs	Update partitioned KV example for synchronous queueing + optional per-record ack.
bindings/python/src/write_handle.rs	Add Python WriteResultHandle with wait() for per-record ack.
bindings/python/src/upsert.rs	Make Python upsert/delete synchronous and return WriteResultHandle; keep flush() async.
bindings/python/src/table.rs	Make Python append APIs return WriteResultHandle; convert flush() to async/awaitable.
bindings/python/src/lib.rs	Export/register WriteResultHandle.
bindings/python/example/example.py	Update Python example to reflect synchronous queueing and awaiting flush()/handle.wait().
bindings/cpp/src/lib.rs	Remove runtime blocking for append queueing; keep blocking for waiting/flush.
README.md	Update Rust snippet for synchronous queueing and add flush.

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[fresh-borzoni]

fixed failing tests, should be fine now

[luoyuxia]

@fresh-borzoni Thanks for the pr. LGTM!