[C-Achard]

Scope

Copies deeplabcut/core/config/ and DLCDeprecationWarning from DeepLabCut dev (14b9c497d). The code is unchanged apart from import paths and licence headers. DeepLabCut will then import them from here. Same content as DeepLabCut/DLClibrary#56, plus reject_reserved_keys (added on dev after v3.0.2).

Moved

• dlccore/config/: base_config (DLCBaseConfig, DLCVersionedConfig), project_config (ProjectConfig), versioning, validation, and from utils the functions read_config_as_dict, write_config, get_yaml_loader, get_yaml_dumper, resolve_alias, resolve_aliases_in_dict, normalize_for_serialization, pretty_print.
• dlccore/deprecation.py: DLCDeprecationWarning only.
• tests/config/: DeepLabCut's tests/core/config/, minus the tests of the functions listed below. The openfield-Pranav-2018-10-30/config.yaml fixture is copied verbatim from DeepLabCut's examples/.
• New dependencies: pydantic>=2.1,<3, numpy>=1.22.4 (DeepLabCut's floor), ruamel-yaml>=0.16, typing-extensions.

Not moved

deeplabcut/core/config/utils.py

Function	Why
read_config	Writes back to disk on read (engine, project_path, detector defaults); ideally reading in dlccore should not write. Used in 51 DeepLabCut files.
write_project_config	Falls back to unvalidated write; may be best to review before moving.
edit_config	Writes without validation; to be reviewed before it moves.
create_config_template	Deprecated since 3.0.1; uses DeepLabCut's @deprecated.
create_config_template_3d, write_config_3d, write_config_3d_template	3D, out of scope for this PR.
ensure_plain_config	Adapts DeepLabCut's call sites; will import DLCBaseConfig from here.

deeplabcut/core/deprecation.py: DeprecationInfo, @deprecated and @renamed_parameter stay, used in 27 DeepLabCut files. Only the class DLCDeprecationWarning moves since resolve_alias raises it.
DeepLabCut imports it back, so that existing filters and pytest.warns still match.
dlccore does not gain packaging, which only DeprecationInfo needs.
We could move the rest of deprecation-related code separately.

PoseConfig migrations: the two placeholder PoseConfig migrations in versioning (both no-ops) stay in DeepLabCut.

Not moved for now

• PoseConfig: its schema is a candidate for dlccore, kept alongside ProjectConfig as suggested on DLClibrary#56, but builders depend on DeepLabCut's runtime (pose templates, transforms, model zoo). I suggest a separate PR in any case.
• Lint is not applied: the copied files are excluded from ruff (lint and format) in pyproject.toml, so they diff cleanly against DeepLabCut. Lint fixes come in a separate PR; until then it's a strict xfail.
• No behavior changes: ProjectConfig.from_yaml still resolves project_path in memory. The readers that move (read_config_as_dict, from_yaml) do not write in DeepLabCut either; the one that writes back, read_config, stays.
• Per-type config versions: there is still one shared CURRENT_CONFIG_VERSION, so a ProjectConfig version bump still forces a PoseConfig migration.

[deruyter92]

Thanks for re-opening on this repository. I'll give it a thorough review