odb: add write_packfile, for_each_unique_abbrev, convert_object_id #27083

Job	Run time
config	8s
fuzz smoke test	1m 25s
win build	4m 48s
rust-analysis	1m 55s
static-analysis	5m 24s
win+Meson build	5m 55s
documentation	7m 53s
sparse	3m 39s
win+VS build	0s
osx-reftable (macos-14)	16m 8s
osx-clang (macos-14)	21m 10s
osx-meson (macos-14)	21m 22s
osx-gcc (macos-14)	24m 28s
linux-TEST-vars (ubuntu:20.04)	12m 8s
linux-reftable (ubuntu:rolling)	14m 7s
linux-sha256 (ubuntu:rolling)	14m 25s
linux-reftable-leaks (ubuntu:rolling)	26m 59s
fedora-breaking-changes-meson (fedora:latest)	10m 0s
linux-leaks (ubuntu:rolling)	23m 39s
linux-asan-ubsan (ubuntu:rolling)	35m 59s
linux-musl-meson (alpine:latest)	9m 9s
linux-breaking-changes (ubuntu:rolling)	13m 17s
linux-meson (ubuntu:rolling)	14m 10s
linux32 (i386/ubuntu:focal)	8m 26s
almalinux-8 (almalinux:8)	10m 2s
debian-11 (debian:11)	10m 46s
win+VS test	0s
win test (3)	7m 9s
win test (5)	7m 6s
win test (6)	7m 43s
win test (2)	9m 7s
win test (9)	11m 20s
win test (7)	6m 55s
win test (4)	12m 56s
win test (0)	6m 35s
win test (1)	7m 53s
win test (8)	4m 55s
win+Meson test (0)	10m 45s
win+Meson test (2)	8m 30s
win+Meson test (4)	8m 37s
win+Meson test (1)	9m 56s
win+Meson test (7)	7m 0s
win+Meson test (9)	10m 29s
win+Meson test (3)	6m 39s
win+Meson test (8)	8m 13s
win+Meson test (6)	11m 41s
win+Meson test (5)	7m 57s
	8h 8m 48s

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