Default `map_size` can cause problems

[Andrew-S-Rosen]

I am running a minimal example with the development version of ALIGNN and am getting back the following:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\github\alignn\alignn\train_alignn.py", line 459, in <module>
    train_for_folder(
  File "C:\github\alignn\alignn\train_alignn.py", line 373, in train_for_folder
    ) = get_train_val_loaders(
        ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\github\alignn\alignn\data.py", line 388, in get_train_val_loaders
    get_torch_dataset(
  File "C:\github\alignn\alignn\lmdb_dataset.py", line 155, in get_torch_dataset
    env = lmdb.open(tmp_name, map_size=int(map_size))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lmdb.Error: Bval_data: There is not enough space on the disk.

I had to hard-code the map_size directly to make it fit in memory, reducing it from 1000000000000.0 to something smaller (I used 10737418240). However, I don't think there is a way to access this variable programmatically.

For a minimal reproducible example, see #188. I am running this on a Windows local machine.