26.0.0rc0: DatasetFile ids for snapshot tree traversal

26.0.0rc0 uses DatasetFile ids for snapshot tree traversal following the openneuro 5.0.0 release.

What's Changed

• DOC: Add CITATION.cff file with OHBM 2026 abstract reference by @jhlegarreta in #31
• STY: Conform to ruff style by @jhlegarreta in #32
• MNT: Bump miscellaneous GitHub action versions by @jhlegarreta in #33
• DOC: Make autodoc signature formatting robust for typing.TypeVar by @jhlegarreta in #34
• FIX: Use DatasetFile ids for snapshot tree traversal by @jhlegarreta in #39

Full Changelog: 25.0.0rc2...26.0.0rc0