cache-tree: use parse_int_from_buf()

In c4c9089 (cache-tree: avoid strtol() on non-string buffer,
2025-11-18) we wrote an ad-hoc integer parser which did not detect
overflow. This wasn't too big a problem, since the original use of
strtol() did not do so either. But now that we have a more robust
parsing function, let's use that. It reduces the amount of code and
should catch more cases of malformed entries.

I kept our local parse_int() wrapper here, since it handles management
of our ptr/len pair (rather than doing it inline in the entry parser of
read_one()).

Author: peff

cache-tree.c

@@ -16,6 +16,7 @@
 #include "promisor-remote.h"
 #include "trace.h"
 #include "trace2.h"
+#include "parse.h"
 
 #ifndef DEBUG_CACHE_TREE
 #define DEBUG_CACHE_TREE 0
@@ -550,32 +551,13 @@ void cache_tree_write(struct strbuf *sb, struct cache_tree *root)
 
 static int parse_int(const char **ptr, unsigned long *len_p, int *out)
 {
-	const char *s = *ptr;
-	unsigned long len = *len_p;
-	int ret = 0;
-	int sign = 1;
-
-	while (len && *s == '-') {
-		sign *= -1;
-		s++;
-		len--;
-	}
-
-	while (len) {
-		if (!isdigit(*s))
-			break;
-		ret *= 10;
-		ret += *s - '0';
-		s++;
-		len--;
-	}
+	const char *ep;
 
-	if (s == *ptr)
+	if (!parse_int_from_buf(*ptr, *len_p, &ep, out))
 		return -1;
 
-	*ptr = s;
-	*len_p = len;
-	*out = sign * ret;
+	*len_p -= ep - *ptr;
+	*ptr = ep;
 	return 0;
 }