Handling Duplicate Changes in PushPull Logic

[kokodak]

What happened:

In the scenario depicted in the provided image, there are instances where duplicate changes are not being filtered correctly.
This leads to a violation of idempotency for duplicate operations, resulting in unintended consequences.

When attempting to reproduce this issue locally, it can be observed as follows:

Screen.Recording.2024-09-05.at.11.25.41.PM.mov

The main cause of this issue is that when the PushPull logic partially fails, it is in an environment where atomicity is not ensured.

To solve this problem, we need to consider additional validation methods beyond ClientSeq to validate whether the change already exists.

What you expected to happen:
The system should effectively filter out duplicate changes to maintain idempotency and prevent unintended results.

How to reproduce it (as minimally and precisely as possible):

1. Request PushPull API
2. Failed to reflect ClientInfo in the database
3. Client didn't receive an error response
4. Re-request PushPull API

Anything else we need to know?:
Related to #805

Environment:

• Operating system:
• Browser and version:
• Yorkie version (use yorkie version): 0.5.0
• Yorkie JS SDK version: