Memorgy Overload when treating systems with large PL

[AsymmetryChou]

Describe the bug

A bug report from @Lonya0.
When treating systems with large principal layers, the current version DPNEGF would raise memory overload. This is a bug due to the default setting of njobs in self-energy calculation. An automatic njob determination mechanism is necessary.

Expected behavior

No response

To Reproduce

No response

Environment

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Additional Context

No response

[AsymmetryChou]

For now, this issue has been solved in #47 with an auto-memory detector to determine the safe n_jobs in joblibs.