### What problem does this PR solve?
Markdown extraction currently applies custom delimiters before
respecting fenced code blocks. When a delimiter such as a newline is
configured, fenced code can be split into separate chunks, and longer
outer fences can be closed incorrectly by shorter nested fences.
This PR keeps the fix intentionally narrow for the Markdown chunking
discussion in #15482:
- preserve fenced code blocks when delimiter-based extraction is used
- support both backtick and tilde fences
- respect fence length so longer outer fences can contain shorter inner
fences
- keep delimiter splitting unchanged outside fenced blocks
Refs #15482
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### Testing
- `ruff check deepdoc/parser/markdown_parser.py
test/unit_test/deepdoc/parser/test_markdown_parser.py`
- `python3 run_tests.py -t
test/unit_test/deepdoc/parser/test_markdown_parser.py`
### What problem does this PR solve?
Fixes markdown tables being parsed twice (once as markdown and again as
generated HTML), which caused duplicate table chunks in the chunk list
UI.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
Now markdown table extractor supports <table ...>. #10966
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
issue:
[#10890](https://github.com/infiniflow/ragflow/issues/10890)
change：
enhance delimiters in markdown parser
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
Fix context loss caused by separating markdown tables from original
text. #6871, #8804.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
Enhance the recognition of both borderless and bordered Markdown tables.
Add support for extracting HTML tables, including various scenarios with
nested HTML tags. Improve performance by using conditional checks to
reduce unnecessary regular expression matching.
### What problem does this PR solve?
Optimize the table extraction logic in the Markdown parser:
Enhance the recognition of both borderless and bordered Markdown tables.
Add support for extracting HTML tables, including various scenarios with
nested HTML tags.
Improve performance by using conditional checks to reduce unnecessary
regular expression matching.
### Type of change
- [x] Performance Improvement
Co-authored-by: wenju.li <wenju.li@deepctr.cn>
### What problem does this PR solve?
Support extracting table for markdown file in general parser
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
