[meson] set default context_alignment to cache_line_size

meson_options.txt

@@ -256,7 +256,7 @@ option(
   type: 'combo',
   description: 'Use the select mechanism to determine the alignment of contexts',
   choices: ['none', 'cache_line_size', 'page_size'],
-  value: 'none',
+  value: 'cache_line_size',
 )
 option(
   'assume_cache_line_size',