BSD StrictProvenance minimum allocation size 16M

This will serve as the granularity with which we store authority
pointers in the (forthcoming) authmap, so 4K is almost surely too small.
16M is, admittedly, chosen out of a hat.

src/snmalloc/pal/pal_bsd_aligned.h

@@ -23,7 +23,8 @@ namespace snmalloc
     static constexpr uint64_t pal_features =
       AlignedAllocation | PALBSD<OS>::pal_features;
 
-    static SNMALLOC_CONSTINIT_STATIC size_t minimum_alloc_size = 4096;
+    static SNMALLOC_CONSTINIT_STATIC size_t minimum_alloc_size =
+      aal_supports<StrictProvenance> ? 1 << 24 : 4096;
 
     /**
      * Reserve memory at a specific alignment.