[Code scan] Remote job submission crashes when resources are omitted

Source: Codex global repository scan of deepmodeling/dpti at commit b719828e7eeb571bd26411430197cd74ea78e38c.
Project: https://github.com/orgs/deepmodeling/projects/27

Problem
`_set_default_resource(None)` creates a local dict but does not return it. Public remote-job script generation paths call `_set_default_resource(resources)` or `_set_default_resource(res)` and then immediately dereference the original argument, which is still `None`. Omitted resources therefore crash instead of using defaults.

Code references
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/RemoteJob.py#L18
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/RemoteJob.py#L36
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/RemoteJob.py#L236
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/RemoteJob.py#L347
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/RemoteJob.py#L479

Reproduction
Call `_make_script(..., resources=None)` on `CloudMachineJob`, or `_make_script(..., res=None)` on `SlurmJob` or `PBSJob`.

Expected result
Default resources should be returned and assigned before any dictionary access, or `None` should be rejected with a clear validation error.

Start in dpti/lib/RemoteJob.py at _set_default_resource and the _make_script methods referenced for CloudMachineJob, SlurmJob, and PBSJob. Reproduce the failure with resources=None or res=None, then verify that omitted resources no longer crash and either use defaults or produce the documented validation error.

Written by the indexing model from the issue text.