odb: add write_packfile, for_each_unique_abbrev, convert_object_id #27084

Job	Run time
config	7s
fuzz smoke test	1m 13s
win+VS build	0s
win build	5m 36s
win+Meson build	5m 45s
documentation	8m 1s
static-analysis	5m 27s
rust-analysis	1m 34s
osx-clang (macos-14)	19m 33s
sparse	3m 33s
osx-gcc (macos-14)	18m 9s
osx-reftable (macos-14)	17m 37s
osx-meson (macos-14)	23m 16s
linux32 (i386/ubuntu:focal)	8m 45s
almalinux-8 (almalinux:8)	9m 27s
linux-asan-ubsan (ubuntu:rolling)	33m 11s
linux-musl-meson (alpine:latest)	8m 59s
linux-reftable (ubuntu:rolling)	14m 48s
linux-TEST-vars (ubuntu:20.04)	12m 50s
linux-breaking-changes (ubuntu:rolling)	13m 6s
debian-11 (debian:11)	10m 44s
win+VS test	0s
linux-sha256 (ubuntu:rolling)	14m 28s
fedora-breaking-changes-meson (fedora:latest)	10m 3s
linux-reftable-leaks (ubuntu:rolling)	29m 34s
linux-leaks (ubuntu:rolling)	24m 41s
linux-meson (ubuntu:rolling)	11m 51s
win test (5)	7m 36s
win test (4)	10m 45s
win test (3)	7m 39s
win test (6)	7m 22s
win test (2)	9m 12s
win test (7)	7m 7s
win test (8)	5m 6s
win test (9)	10m 47s
win test (0)	6m 23s
win test (1)	7m 44s
win+Meson test (1)	14m 51s
win+Meson test (0)	12m 2s
win+Meson test (5)	8m 3s
win+Meson test (7)	7m 38s
win+Meson test (3)	6m 0s
win+Meson test (2)	8m 39s
win+Meson test (4)	7m 42s
win+Meson test (8)	8m 57s
win+Meson test (9)	10m 49s
win+Meson test (6)	11m 23s
	8h 8m 3s

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