pack-objects(check_pack_inflate()): use size_t instead of unsigned long

pack-objects(check_pack_inflate()): use size_t instead of unsigned long

`write_reuse_object()` learned to track its packed-object size as
`size_t` in 606c192380 (odb, packfile: use size_t for streaming
object sizes, 2026-05-08), but the comparison sink it feeds,
`check_pack_inflate()`, still takes the expected decompressed size
as `unsigned long`. The call site bridges the mismatch with
`cast_size_t_to_ulong()`, which on Windows turns a >4 GiB object
into an immediate die().

That function only uses `expect` once: as the right-hand side of a
`stream.total_out == expect` equality test against zlib's counter.
zlib's own `total_out` counter is `uLong` and is therefore still
32-bit-bound on Windows. Widening `expect` to `size_t` cannot fix that,
but it is a strict improvement nonetheless: instead of dying outright,
an oversized object now simply makes the equality fail and lets
`write_reuse_object()` fall back to `write_no_reuse_object()`, which
decompresses and re-deflates the content (and which the larger
pack-objects widening series targets separately).

Drop the `cast_size_t_to_ulong()` shim at the call site now that
the receiving parameter speaks the same type as `entry_size`.

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