Add __version__ identifier

- `lalib.__version__` is dynamically assigned
- the format is "x.y.z[.dev0|aN|bN|rcN|.postM]"
  where x, y, z, M, and N are non-negative integers
  + x, y, and z model the "major", "minor", and "patch"
    parts of semantic versioning
    (See: https://semver.org/#semantic-versioning-200)
  + M is a single digit and N either 1 or 2
  => This complies with (a strict subset of) PEP440
- add unit tests for the `__version__` identifier

noxfile.py

@@ -152,8 +152,10 @@ def test(session: nox.Session) -> None:
     install_unpinned(session, "-e", ".")  # "-e" makes session reuseable
     install_pinned(
         session,
+        "packaging",
         "pytest",
         "pytest-cov",
+        "semver",
     )
 
     args = session.posargs or (
@@ -162,8 +164,7 @@ def test(session: nox.Session) -> None:
         TESTS_LOCATION,
     )
 
-    # Code 5 is temporary as long as there are no tests
-    session.run("pytest", *args, success_codes=[0, 5])
+    session.run("pytest", *args)
 
 
 def start(session: nox.Session) -> None: