diff-delta: widen `struct delta_index`' size fields to `size_t`

Preparation for widening the delta-encoding API to `size_t` in
subsequent commits, which is what lets pack-objects drop the
`cast_size_t_to_ulong()` shims that 606c192380 (odb, packfile: use
size_t for streaming object sizes, 2026-05-08) had to leave behind in
`get_delta()` and `try_delta()` because their downstream consumers were
still narrow.

The struct is private to diff-delta.c, so widening its fields in
isolation is a no-op at runtime: the values stored continue to fit in 32
bits on Windows because the public API around it still truncates.
Splitting it out keeps the API-change commit focused on caller updates.

Since the `memsize` attribute is returned by the `sizeof_delta_index()`
function verbatim, that function's return type is adjusted, too.

Assisted-by: Opus 4.7
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

0 files changed, 0 insertions, 0 deletions