feat: add `fmt_flag()` method #2162

Job	Run time
test-pandas	42s
build (3.9)	1m 21s
Test for saving table image with browser	2m 29s
build (3.10)	1m 6s
test-windows	4m 32s
build (3.11)	1m 23s
build (3.12)	1m 17s
build (3.13)	1m 41s
Release to pypi	0s
	14m 31s

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