Check -l<=m<=l for 2<=l<=Lmax exist
Currently lvcnrcheck does not verify that all the m-mode datasets exist for -l<=m<=l for 2<=l<=Lmax.
A candidate solution to this is to replace lvcnrpy/format/specs.py#L595-597 with a cross-key dependant list (dependant on Lmax) of the expected mode datasets rather than a glob of the datasets that exist. As such, this will raise an err.Missing when format spec mandated modes are missing.
I believe this is the shortest solution that reuses existing code to solve this issue.