Dcnum

- fix: protected features (e.g. time, frame) were not included in ouptut
files when the input file was basin-based
- ref: increment DCNUM_PPID_GENERATION to 6

- fix: correctly raise KeyError for missing image-based feature from
`HDF5Data._image_cache`

- fix: properly convert variable-length string logs in `copy_metadata`

- fix: wrong event count in logs
- ref: np.product is deprecated in numpy 2.0

- feat: support writing file-based HDF5 basins (11)
- feat: support reading file-based HDF5 basins (11)
- feat: implement `create_with_basins` convenience method (11)
- fix: correctly support passing an ndarray to BackgroundSparseMed
instead of an input file path
- fix: BackgroundSparseMed did not work for datasets of length < 100
- fix: bad f-string in BackgroundSparseMed
- enh: create a default basin-based output file for background computation
- ref: unite initialization code of background comptuers in base class
- ref: define context managers of background comptuers in base class
- ref: remove functools.cache decorator from HDF5Data
- tests: add tests for BackgroundSparseMed

- fix: background computation with sparsemed did not work
- enh: support passing paths as strings to Background class