Working dir emptiness check

[liamhuber]

Just very minor convenience changes to the filesystem stuff: adds a property DirectoryObject.is_empty that checks agains length, and modifies deletion so you can choose to only delete if it's empty: DirectoryObject.(self, only_if_empty: bool = False)

[github-actions]

👈 Launch a binder notebook on branch pyiron/pyiron_workflow/working_dir

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.01% (target: -1.00%)	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (f11d7ea)	2569	2192	85.33%
Head commit (85f153d)	2572 (+3)	2195 (+3)	85.34% (+0.01%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#157)	5	5	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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