fix: merge streamed tool results per call

[he-yufeng]

Fixes #8028.

Modifications / 改动点

• Collects multiple CallToolResult chunks produced by an async-generator tool execution and appends a single tool result block for the original tool_call_id.

• Keeps cached image handling and tool hook behavior in the existing flow.

• Adds a regression test that yields two CallToolResult values for one tool call and verifies AstrBot stores one tool message with both partial results.

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

Verification commands run locally on Windows:

uv run pytest tests\test_tool_loop_agent_runner.py::test_async_generator_tool_results_share_one_tool_call_id -q
# 1 passed

uv run pytest tests\test_tool_loop_agent_runner.py -q
# 30 passed

uv run ruff check astrbot\core\agent\runners\tool_loop_agent_runner.py
# All checks passed

uv run ruff format astrbot\core\agent\runners\tool_loop_agent_runner.py tests\test_tool_loop_agent_runner.py --check
# 2 files already formatted

uv run python -m py_compile astrbot\core\agent\runners\tool_loop_agent_runner.py tests\test_tool_loop_agent_runner.py
# passed

git diff --check
# passed

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Checklist / 检查清单

• 😊 If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc.
  / 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。

• 👀 My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above.
  / 我的更改经过了良好的测试，并已在上方提供了“验证步骤”和“运行截图”。

• 🤓 I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml.
  / 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到 requirements.txt 和 pyproject.toml 文件相应位置。

• 😮 My changes do not introduce malicious code.
  / 我的更改没有引入恶意代码。

Summary by Sourcery

Merge multiple streamed tool execution results for a single tool call into one consolidated tool message.

Bug Fixes:

• Ensure multiple CallToolResult chunks from async generator tools are combined into a single provider tool message per tool_call_id instead of producing separate messages.

Tests:

• Add regression test verifying that two streamed CallToolResult yields for one tool_call_id are stored as a single tool message containing both partial results.

[gemini-code-assist]

Code Review

This pull request updates the tool execution logic to aggregate multiple results from a single tool call into one message. By collecting partial results in a list and joining them before final processing, the runner now ensures that streamed or multi-yield tool outputs are associated with a single tool call ID. Additionally, a new test case and a mock executor were added to verify this aggregation behavior. I have no feedback to provide.