[raster] Reduce buffer size cap

Lower HB_RASTER_MAX_BUFFER_SIZE from 1<<30 to 1<<24 so the shared
raster image / clip-mask limit meaningfully constrains pathological
fuzzer inputs instead of allowing timeout-scale temporary buffers.

Assisted-by: OpenAI Codex

src/hb-limits.hh

diff --git a/src/hb-limits.hh b/src/hb-limits.hh
index 8dc7b1a..5b9954d 100644
--- a/src/hb-limits.hh
+++ b/src/hb-limits.hh
@@ -113,7 +113,7 @@
 #endif
 
 #ifndef HB_RASTER_MAX_BUFFER_SIZE
-#define HB_RASTER_MAX_BUFFER_SIZE ((size_t) 1 << 30)
+#define HB_RASTER_MAX_BUFFER_SIZE ((size_t) 1 << 24)
 #endif