pack-objects: drop the two tree-walk casts in the preferred-base path

With init_tree_desc() widened in the prior commit, the
size_t-returning odb_read_object_peeled() call in
add_preferred_base() and odb_read_object() call in pbase_tree_get()
can both flow straight through to init_tree_desc() and into the
pbase_tree_cache. Widen pbase_tree_cache.tree_size and the two
local size variables to size_t, drop the size_st bridges, and drop
the two cast_size_t_to_ulong() shims.

This was the last pair of cast_size_t_to_ulong() call sites in
builtin/pack-objects.c, completing the >4 GiB-objects work in that
file that this branch and its predecessors have been pursuing.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

builtin/pack-objects.c

@@ -1919,7 +1919,7 @@ struct pbase_tree_cache {
 	int ref;
 	int temporary;
 	void *tree_data;
-	unsigned long tree_size;
+	size_t tree_size;
 };
 
 static struct pbase_tree_cache *(pbase_tree_cache[256]);
@@ -1946,8 +1946,7 @@ static struct pbase_tree_cache *pbase_tree_get(const struct object_id *oid)
 {
 	struct pbase_tree_cache *ent, *nent;
 	void *data;
-	unsigned long size;
-	size_t size_st = 0;
+	size_t size;
 	enum object_type type;
 	int neigh;
 	int my_ix = pbase_tree_cache_ix(oid);
@@ -1975,8 +1974,7 @@ static struct pbase_tree_cache *pbase_tree_get(const struct object_id *oid)
 	/* Did not find one.  Either we got a bogus request or
 	 * we need to read and perhaps cache.
 	 */
-	data = odb_read_object(the_repository->objects, oid, &type, &size_st);
-	size = cast_size_t_to_ulong(size_st);
+	data = odb_read_object(the_repository->objects, oid, &type, &size);
 	if (!data)
 		return NULL;
 	if (type != OBJ_TREE) {
@@ -2130,16 +2128,14 @@ static void add_preferred_base(struct object_id *oid)
 {
 	struct pbase_tree *it;
 	void *data;
-	unsigned long size;
-	size_t size_st = 0;
+	size_t size;
 	struct object_id tree_oid;
 
 	if (window <= num_preferred_base++)
 		return;
 
 	data = odb_read_object_peeled(the_repository->objects, oid,
-				      OBJ_TREE, &size_st, &tree_oid);
-	size = cast_size_t_to_ulong(size_st);
+				      OBJ_TREE, &size, &tree_oid);
 	if (!data)
 		return;