index-pack: retain child bases in delta cache #28039

Job	Run time
config	7s
fuzz smoke test	1m 16s
win build	5m 28s
static-analysis	5m 31s
win+Meson build	4m 48s
osx-clang (macos-14)	6h 0m 18s
sparse	3m 15s
osx-reftable (macos-14)	32m 21s
osx-meson (macos-14)	45m 51s
documentation	7m 36s
osx-gcc (macos-14)	6h 0m 18s
rust-analysis	1m 30s
win+VS build	0s
linux-leaks (ubuntu:rolling)	49m 16s
linux-TEST-vars (ubuntu:20.04)	24m 4s
linux-sha256 (ubuntu:rolling)	18m 43s
fedora-breaking-changes-meson (fedora:latest)	17m 38s
almalinux-8 (almalinux:8)	18m 8s
linux-musl-meson (alpine:latest)	21m 40s
linux32 (i386/ubuntu:focal)	6h 0m 3s
linux-reftable (ubuntu:rolling)	24m 28s
linux-reftable-leaks (ubuntu:rolling)	47m 3s
linux-breaking-changes (ubuntu:rolling)	24m 28s
debian-11 (debian:11)	25m 15s
linux-asan-ubsan (ubuntu:rolling)	1h 7m 42s
linux-meson (ubuntu:rolling)	25m 5s
win+VS test	0s
win+Meson test (4)	7m 24s
win+Meson test (8)	9m 1s
win+Meson test (7)	7m 6s
win+Meson test (5)	6m 42s
win+Meson test (6)	10m 27s
win+Meson test (0)	8m 33s
win+Meson test (9)	6m 42s
win+Meson test (2)	1h 0m 59s
win+Meson test (3)	10m 31s
win+Meson test (1)	9m 49s
win test (0)	10m 45s
win test (5)	10m 36s
win test (4)	16m 28s
win test (2)	9m 40s
win test (1)	7m 20s
win test (7)	5m 0s
win test (3)	59m 38s
win test (6)	8m 40s
win test (9)	5m 18s
win test (8)	6m 32s
	1d 6h 29m 3s

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