misc/random: add xoshiro random number implementation

Add xoshiro as a PRNG implementation instead of relying
on srand() and rand() from the C standard library. This,
in particular, lets us avoid platform-defined behavior with
respect to threading.

meson.build

@@ -134,6 +134,7 @@ sources = files(
     'misc/json.c',
     'misc/natural_sort.c',
     'misc/node.c',
+    'misc/random.c',
     'misc/rendezvous.c',
     'misc/thread_pool.c',
     'misc/thread_tools.c',