replace sprintf usage with snprintf

Even though this specific usage is safe, it is, arguably, not great to
be using sprintf in year 2024. snprintf is portable enough this
days. Thanks goes to OSX headers that warn about sprintf loudly enough
to be noticed.

src/malloc_extension.cc

diff --git a/src/malloc_extension.cc b/src/malloc_extension.cc
index 5f2ec2c..c9819ba 100644
--- a/src/malloc_extension.cc
+++ b/src/malloc_extension.cc
@@ -263,7 +263,7 @@
   }
 
   char label[32];
-  sprintf(label, "heap_v2/%d", sample_period);
+  snprintf(label, sizeof(label), "heap_v2/%d", sample_period);
   PrintHeader(writer, label, entries);
   for (void** entry = entries; Count(entry) != 0; entry += 3 + Depth(entry)) {
     PrintStackEntry(writer, entry);