Remove all instances of static_cast<size_t>(1).

In preparation for removing magic numbers, simplify code that is
computing masks with a single bit set.

src/mem/sizeclasstable.h

@@ -30,8 +30,7 @@ namespace snmalloc
           bits::from_exp_mant<INTERMEDIATE_BITS, MIN_ALLOC_BITS>(sizeclass);
 
         size_t alignment = bits::min(
-          static_cast<size_t>(1) << bits::ctz_const(size[sizeclass]),
-          OS_PAGE_SIZE);
+          bits::one_at_bit(bits::ctz_const(size[sizeclass])), OS_PAGE_SIZE);
         cache_friendly_mask[sizeclass] = (alignment - 1);
         inverse_cache_friendly_mask[sizeclass] = ~(alignment - 1);
       }