Local input concurrency control

[cathyzbn]

Describe your changes

Added set_local_input_concurrency and get_local_input_concurrency for users to control input concurrency changes.

Backward/forward compatibility checks

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Check these boxes or delete any item (or this section) if not relevant for this PR.

• Client+Server: this change is compatible with old servers
• Client forward compatibility: this change ensures client can accept data intended for later versions of itself

Note on protobuf: protobuf message changes in one place may have impact to
multiple entities (client, server, worker, database). See points above.

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Changelog

Added modal.experimental.set_local_input_concurrency and modal.experimental.get_local_input_concurrency for input concurrency control

[mwaskom]

Closing as stale, but can revisit later.