Replaced tn/bn prefixes with an actual dependency system in tests/benches

The previous system of relying on test name prefixes for ordering was
simple, but organizing tests by dependencies and topologically sorting
during compilation is 1. more flexible and 2. simplifies test names,
which get typed a lot.

Note these are not "hard" dependencies, each test suite should work fine
in isolation. These "after" dependencies just hint an ordering when all
tests are ran.

As such, it's worth noting the tests should NOT error of a dependency is
missing. This unfortunately makes it a bit hard to catch typos, but
allows faster compilation of a subset of tests.

---

To make this work the way tests are linked has changed from using custom
linker section (fun linker magic!) to a weakly linked array appended to
every source file (also fun linker magic!).

At least with this method test.py has strict control over the test
ordering, and doesn't depend on 1. the order in which the linker merges
sections, and 2. the order tests are passed to test.py. I didn't realize
the previous system was so fragile.

runners/bench_runner.h

@@ -74,6 +74,9 @@ struct bench_suite {
     size_t case_count;
 };
 
+extern const struct bench_suite *const bench_suites[];
+extern const size_t bench_suite_count;
+
 
 // deterministic prng for pseudo-randomness in benches
 uint32_t bench_prng(uint32_t *state);