gh-99880: document rounding mode for new-style formatting #131124

Job	Run time
Change detection / Compute changed files	13s
Windows ${{ ((fromJSON(matrix.free-threading) && '(free-threading)') \|\| '') }}	0s
Check if generated files are up to date	0s
Check if Autoconf files are up to date	0s
Windows MSI${{ '' }}	0s
macOS ${{ ((fromJSON(matrix.free-threading) && '(free-threading)') \|\| '') }}	0s
Ubuntu ${{ ((fromJSON(matrix.free-threading) && '(free-threading)') \|\| '') }}	0s
Ubuntu SSL tests with OpenSSL	0s
WASI	0s
Address sanitizer	0s
Thread sanitizer	0s
Thread sanitizer (free-threading)	0s
CIFuzz	0s
Hypothesis tests on Ubuntu	0s
Docs / Docs (Oldest Sphinx)	2m 18s
Docs / Docs	2m 14s
Docs / Doctest	28m 1s
All required checks pass	3s
	32m 49s

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