patch-delta: use size_t for sizes

`patch_delta()` takes the source and delta sizes by value and writes
back the reconstructed target size through an `unsigned long *`.  That
datatype cannot represent a value that exceeds 4 GiB on systems where
`unsigned long` is 32-bit (notably 64-bit Windows builds), though, even
though the delta encoding itself, the on-disk layout, and the in-memory
buffers happily carry such sizes. A `size_t` companion to
`get_delta_hdr_size()`, `get_delta_hdr_size_sz()`, was introduced in
17fa077596 (delta, packfile: use size_t for delta header sizes,
2026-05-08) precisely so that `patch_delta()` could be widened without
changing the on-the-wire decoding helper's signature.

Widen `patch_delta()`'s three size parameters to `size_t` and switch
its internal use of `get_delta_hdr_size()` to the `_sz` variant.
Then propagate the wider type through the callers.

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

packfile.c

@@ -1964,10 +1964,8 @@ void *unpack_entry(struct repository *r, struct packed_git *p, off_t obj_offset,
 			      (uintmax_t)curpos, p->pack_name);
 			data = NULL;
 		} else {
-			unsigned long sz;
 			data = patch_delta(base, base_size, delta_data,
-					   delta_size, &sz);
-			size = sz;
+					   delta_size, &size);
 
 			/*
 			 * We could not apply the delta; warn the user, but