Refactor base_url handling #113

Job	Run time
sdist	14s
macos (macos-latest, aarch64)	56s
macos (macos-15-intel, x86_64)	1m 54s
windows (windows-latest, x86, x86)	2m 58s
windows (windows-11-arm, aarch64, arm64)	3m 29s
musllinux (ubuntu-22.04, x86_64)	1m 28s
windows (windows-latest, x64, x64)	3m 17s
linux (ubuntu-22.04, s390x)	2m 13s
musllinux (ubuntu-22.04, aarch64)	1m 34s
musllinux (ubuntu-22.04, x86)	1m 28s
linux (ubuntu-22.04, ppc64le)	2m 10s
linux (ubuntu-22.04, x86_64)	1m 37s
musllinux (ubuntu-22.04, armv7)	1m 19s
linux (ubuntu-22.04, armv7)	1m 52s
linux (ubuntu-22.04, aarch64)	2m 7s
linux (ubuntu-22.04, x86)	2m 11s
Release	0s
	30m 47s

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