Implement energon prepare with a remote dataset (using local temp)

[voegtlel]

Fixes #91

Implements energon prepare for remote (including media metadata preparation)

[radulescupetru]

I see ValueError: Path msc://default/path_to_s3_dataset is not local error

Preparing filesystem dataset and computing media metadata...
Traceback (most recent call last):
  File "/home/user/miniconda3/envs/conda_env/bin/energon", line 7, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/click/core.py", line 1485, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/click/core.py", line 1406, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/click/core.py", line 1873, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/click/core.py", line 1269, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/click/core.py", line 824, in invoke
    return callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/megatron/energon/tools/prepare_media.py", line 110, in command
    stored = prepare_filesystem_dataset(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/megatron/energon/media/filesystem_prepare.py", line 44, in prepare_filesystem_dataset
    root = root_path.local_path()
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/conda_env/lib/python3.12/site-packages/megatron/energon/epathlib/epath.py", line 258, in local_path
    raise ValueError(f"Path {self} is not local")

There's also a TODO in that method:

Only supporting local file system, because sqlite does not support remote file systems.

TODO: Implement remote file systems. Maybe create locally in tmp then upload?

[voegtlel]

@radulescupetru sorry for taking a while, had other priorities. Now also implemented that for filesystem:// links. Can you try again?