Adds tests for binary functions

Adds a test to check int->bytes works as expected

Split the root test suite 'all-tests' into two sub suites

- 'ulid has the ulid construction tests
- 'binary-utils has tests for the binary stuff

you can run them like so

(fiveam:run! 'cms-ulid/tests::ulid)
(fiveam:run! 'cms-ulid/tests::binary-utils)
(fiveam:run! 'cms-ulid/tests::all-tests)

or , (asdf:test-system 'cms-ulid) will invoke test-op which
runs all tests

NB. while testing this iteratively on the repl, I realised that
the let over the ulid function used to initialise the `last` check
used to implement the time collision avoidance means that the static
ulid check is not idempotent - once we've run the test for the fixed
timestamp once, the ulid constructor will hold onto the fixed time