Two small typing nits in src/alpamayo_r1/common/wandb_utils.py:

- init_wandb declares `key: str` but the body branches on
  `if key is not None`, and the comment "otherwise it will load from
  the home directory" makes clear that None is the supported "use
  cached credentials" path. Type checkers flag any `init_wandb(None,
  ...)` call site, even though that's the documented behavior.
  Update the annotation to `str | None`.

  While here, expand the one-word docstring to actually describe each
  parameter (the function is called from external launchers and was
  previously self-documenting only via the parameter names).

- _save_wandb_id has no return annotation. The function returns None
  (writes to disk and stops). Add `-> None` for consistency with
  `_check_wandb_id` immediately below it (which already has its
  return type annotated).

Pure typing/docstring change. No runtime behavior change.

Signed-off-by: lonexreb <[email protected]>