[ty] Render Google and NumPy docstrings as Markdown

[lerebear]

Summary

Render supported Google and NumPy docstring sections as Markdown for hover and related IDE output. This routes docstrings through a narrow structured-docstring parser after the existing reST rendering pass, covering top-level Parameters/Attributes/Returns/Raises sections while leaving existing parameter-documentation extraction unchanged.

Closes astral-sh/ty#1667

Test Plan

Please see included tests.

[codspeed-hq]

Merging this PR will not alter performance

✅ 67 untouched benchmarks
⏩ 60 skipped benchmarks¹

---

_{Comparing lerebear/push-docstring-markdown-styles (b61f96a) with lerebear/push-usmovrotyxzm (cba0858)}

Footnotes

1. 60 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩