### What problem does this PR solve?
Fixes the PubMed tool always emitting `Authors: Unknown Authors`. The
`safe_find` closure in `_format_pubmed_content` was hardcoded to search
from the article root, so the per-author `LastName`/`ForeName` lookups
never matched.
`safe_find` now accepts an optional `base` node (defaults to `child`,
preserving the existing field lookups), and the author loop passes the
current `<Author>` element.
Closes#16328
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Add test cases
### Testing
Added `test/testcases/test_web_api/test_canvas_app/test_pubmed_unit.py`
covering per-author parsing, intact title/journal/DOI fields, and the
no-authors fallback.
Before: `Authors: Unknown Authors`
After: `Authors: Furqan Khan, Jane Smith`
### What problem does this PR solve?
Add mechanism to check cancellation in Agent.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
issue:
[#6571](https://github.com/infiniflow/ragflow/issues/6571)
change:
include author, journal name, volume, issue, page, and DOI in PubMed
search results
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
Fix invalid COMPONENT_EXEC_TIMEOUT. #10273
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
#9082#6365
<u> **WARNING: it's not compatible with the older version of `Agent`
module, which means that `Agent` from older versions can not work
anymore.**</u>
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
