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[bot]]

:point_left: Launch a binder notebook on branch _pyiron/pyiron_workflow/workingdir

[codacy-production[bot]]

Coverage summary from Codacy

See diff coverage on Codacy

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

Coverage variation details

| | Coverable lines | Covered lines | Coverage | | ------------- | ------------- | ------------- | ------------- | | Common ancestor commit (f11d7ea42075f13598ed9d6eccdb33c996412bfe) | 2569 | 2192 | 85.33% | | | Head commit (85f153d15a0a22f8427a6551ed3bcf716b1d6bc7) | 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: ` - `

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: `/ * 100%`

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