Dclab

- feat: allow nested basins
- feat: implement DCOR basins
- fix: make sure basins are always closed on context exit (238)
- fix: failed to load basin data when port was specified in location
- enh: requests session pooling for fmt_http and fmt_dcor
- enh: implement context manager for RTDCBase
- enh: be forwards-compatible and ignore unsupported basin formats
- ref: new http_utils submodule for managing HTTP connections

- test: tested rtdc_dataset.config.Configuration is pickable (190)
- enh: add dcnum pipeline identifier metadata constants

- fix: default `host` was overriding URL host in fmt_dcor

- enh: register new features area_um_raw, deform_raw, eccentr_prnc,
per_ratio, per_um_raw, sym_x, sym_y
- ref: simplify/cleanup computation of tilt feature

- enh: improve timeout and availability check for fmt_http

- enh: migrate to purely requests-based HTTP file for fmt_http