fix: support cases when there is both field condition and logical operators

[endxxxx]

Description

This PR is fixing a bug , which will result in calling failure or continuous lag when calling the get_memory interface with the mem_cube_id parameter and a filter carrying logical operators such as AND, OR, and NOT.

Related Issue (Required): Fixes #1075

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test Script Or Test Steps (please provide)

def get_memory():
    data = {
      "filter": {
          "and": [
              {
                  "created_at": {
                      "gte": "2026-01-01 20:01:39"
                  }  
              }
          ] # there is a logical operator in the filter
      },
      "mem_cube_id": "xxx",  # there is a mem_cube_id
      "include_preference": True,
      "include_tool_memory": True,
      "page": 1,
      "page_size": 10
    }
    headers = {
        "Content-Type": "application/json",
        "Authorization": f"Token {os.environ['MEMOS_API_KEY']}"
    }
    url = f"{os.environ['MEMOS_BASE_URL']}/get_memory"
    
    res = requests.post(url=url, headers=headers, data=json.dumps(data))

    return res.json()

Checklist

• I have performed a self-review of my own code | 我已自行检查了自己的代码
• I have commented my code in hard-to-understand areas | 我已在难以理解的地方对代码进行了注释
• I have added tests that prove my fix is effective or that my feature works | 我已添加测试以证明我的修复有效或功能正常
• I have created related documentation issue/PR in MemOS-Docs (if applicable) | 我已在 MemOS-Docs 中创建了相关的文档 issue/PR（如果适用）
• I have linked the issue to this PR (if applicable) | 我已将 issue 链接到此 PR（如果适用）
• I have mentioned the person who will review this PR | 我已提及将审查此 PR 的人

Reviewer Checklist

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Made sure Checks passed
• Tests have been provided