### What problem does this PR solve?

This PR introduces Pydantic-based validation for the update dataset HTTP
API, improving code clarity and robustness. Key changes include:
1. Pydantic Validation
2. ​​Error Handling
3. Test Updates
4. Documentation Updates
5. fix bug: #5915

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Documentation Update
- [x] Refactoring

### What problem does this PR solve?

Optimize dataset validation and add function docs

### Type of change

- [x] Refactoring

### What problem does this PR solve?

cover [Delete chat assistant's
sessions](https://ragflow.io/docs/dev/http_api_reference#delete-chat-assistants-sessions)
endpoints

### Type of change

- [x] Add test cases

### What problem does this PR solve?

cover [create session with chat
assistant](https://ragflow.io/docs/dev/http_api_reference#create-session-with-chat-assistant)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [delete chat
assistants](https://ragflow.io/docs/dev/http_api_reference#delete-chat-assistants)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [create chat
assistant](https://ragflow.io/docs/v0.17.2/http_api_reference#create-chat-assistant)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

 Refactor test fixtures and test cases

### Type of change

- [ ] Refactoring test cases

### What problem does this PR solve?

cover [retrieval
chunk](https://ragflow.io/docs/v0.17.2/http_api_reference#retrieve-chunks)
endpoints

### Type of change

- [x]  add test cases

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [update
chunk](https://ragflow.io/docs/v0.17.2/http_api_reference#update-chunk)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [list
chunks](https://ragflow.io/docs/v0.17.2/http_api_reference#list-chunks)
endpoints

### Type of change

- [x] update test cases

### What problem does this PR solve?

Add list chunk checkpoint for the add chunk API

### Type of change

- [x] update test cases

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] update test cases

### What problem does this PR solve?

PR #6194 #6259 #6376

### Type of change

- [x] Update test cases

### What problem does this PR solve?

cover [add
chunk](https://ragflow.io/docs/v0.17.2/http_api_reference#add-chunk)
endpoints

### Type of change

- [x] Add test cases

### What problem does this PR solve?

cover [stop parse
documents](https://ragflow.io/docs/dev/http_api_reference#stop-parsing-documents)
endpoints

### Type of change

- [x] Add test cases

### What problem does this PR solve?

cover [parse
documents](https://ragflow.io/docs/dev/http_api_reference#parse-documents)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [delete
documents](https://ragflow.io/docs/dev/http_api_reference#delete-documents)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [update documents
endpoints](https://ragflow.io/docs/dev/http_api_reference#update-document)

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [download docments
endpoints](https://ragflow.io/docs/dev/http_api_reference#download-document)

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover upload docments endpoints

### Type of change

- [x] add test cases