ENH: Upstream extract_entities and check_pipeline_version BIDS utilities from fMRIPrep

[oesteban]

Summary

fMRIPrep contains general-purpose BIDS utilities in `fmriprep/utils/bids.py` that are not fMRI-specific:

`extract_entities` (lines 350-381)

Extracts common BIDS entities from a file list. Fully general and useful for any BIDS-based tool.

`check_pipeline_version` (lines 292-347)

Checks for version conflicts in existing output directories. Fully general for any *Prep tool that needs to detect output from a different pipeline version.

Code to upstream

• `extract_entities` in `fmriprep/utils/bids.py`
• `check_pipeline_version` in `fmriprep/utils/bids.py`

Rationale

• Both functions are completely modality-agnostic
• Every *Prep tool needs entity extraction and version conflict detection
• Centralizing these avoids divergent implementations

Priority

MEDIUM.