Hierarchy-transformers

Added

- [X] [`feature`] Add `HierarchyTransformerTrainer` that extends `SentenceTransformerTrainer` with step-wise (per batch) loss logging.

Changed

- [X] [`chore`] Refactor all the code with ruff linter.

Significant development to align with `sentence-transformers>=3.4.0.dev0`.

Added

- [X] [`feature`] Add pytest modules for testing.
- [X] [`docs`] Set up [project page](https://krr-oxford.github.io/HierarchyTransformers/).
- [X] [`feature`] Upload HiT datasets on [HuggingFace](https://huggingface.co/Hierarchy-Transformers).
- [X] [`feature`] Re-organise models by setting `v1-random-negatives` and `v1-hard-negatives` revisions on [HuggingFace](https://huggingface.co/Hierarchy-Transformers).

Changed

- [X] [`chore`] Rewrite and reorganise `hierarchy_transformers.models`, `hierarchy_transformers.losses`, and `hierarchy_transformers.evaluation` to to align with `sentence-transformers>=3.4.0.dev`.
- [X] [`chore`] Rewrite dataset processing and loading functions and reorganise everything into `hierarchy_transformers.datasets`.

Removed

- [X] [`chore`] Remove `hierarchy_transformers.models.utils`.

Initial release (should work with `sentence-transformers<3.0.0` ) and bug fix.