ENH: Allow dictionary input for BIDSLayout derivatives parameter to s…

[anushkagupta200615-jpg]

Fixes #1155

Description

This PR introduces the ability to pass a dictionary to the derivatives parameter in BIDSLayout (or layout.add_derivatives()) to map custom names to derivative pipelines.

Previously, PyBIDS strictly extracted the pipeline name from the derivative's base directory name or dataset_description.json. This was inflexible and forced users to query derivatives using potentially messy directory names.

Now, users can pass a dictionary mapping custom names to derivative paths (e.g., layout = BIDSLayout(data_dir, derivatives={'my_clean_pipeline': '/path/to/ugly_pipeline_name_v1.0.0'})). The specified dictionary key will explicitly override the derivative's source_pipeline property, allowing intuitive and clean queries via layout.get(scope='my_clean_pipeline').

Changes Made

• Modified _get_derivative_dirs in src/bids/layout/layout.py to support dict paths, yielding the custom key instead of parsing the directory name.
• Modified add_derivatives in src/bids/layout/layout.py to prevent listify from destroying dictionary structures, and overrode the spawned BIDSLayout's source_pipeline property with the user's custom dictionary key.
• Updated _sanitize_init_args in src/bids/layout/models.py to properly serialize and sanitize dictionary initialization arguments for the layout database.