feat: dataframe download separator #14438

Job	Run time
changes	8s
Test lint and typecheck	2m 6s
ubuntu-latest / Py 3.10 / minimal deps	13m 36s
ubuntu-latest / Py 3.10 / core deps	13m 11s
ubuntu-latest / Py 3.11 / core deps	13m 16s
ubuntu-latest / Py 3.10 / core,optional deps	19m 5s
ubuntu-latest / Py 3.11 / core,optional deps	19m 49s
ubuntu-latest / Py 3.12 / core,optional deps	24m 36s
windows-latest / Py 3.10 / core,optional deps	25m 17s
ubuntu-latest / Py 3.13 / core deps	13m 33s
windows-latest / Py 3.10 / core deps	17m 52s
macos-latest / Py 3.10 / core,optional deps	14m 59s
macos-latest / Py 3.10 / core deps	9m 50s
ubuntu-latest / Py 3.12 / core deps	11m 55s
ubuntu-latest / Py 3.14 / core deps	13m 56s
ubuntu-latest / Py 3.13 / core,optional deps	23m 36s
Test coverage	0s
Test docs	0s
	3h 56m 45s

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