refactor: implement cooperative state machine for range/list operations

[drmingdrmer]

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Summary

refactor: implement cooperative state machine for range/list operations

Fix blocking issue during initialization data transmission.

Problem:

When establishing a watch stream, the meta-service sends large amounts of
initialization data to the client. During this transmission, other events
are blocked until completion, including add-watcher commands.

This creates a deadlock: if initialization data is large, it blocks all
subsequent Dispatcher operations. When a second watch request arrives,
it must wait for the first one to complete sending all initialization data.
Since adding a new watcher requires holding the state machine lock,
multiple concurrent watch requests will block the state machine entirely,
causing timeouts for other requests.

Solution:

Make the process cooperative by not waiting for watch stream transmission
to complete. Instead, queue the add-watcher command and return immediately.
This allows subsequent watch requests to proceed without waiting for previous
initialization data transmissions to finish.

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Refactoring

Related Issues

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This change is 

[drmingdrmer]

This should fix the 4s timeout when meta-service initialize a watch stream with large bunch of initialization data. @everpcpc @bohutang

[bohutang]

LGTM 👍