Cap-anndata

Fixed
- **Python 3.9 Compality**: Fixed type notation in `CapAnnDataDF`.

Added

- **Reader Module**: Introduced `reader.py` with context manager `read_h5ad` and function `read_directly` for reading AnnData files.
- **Join and Merge Methods**: Enhanced methods for joining and merging dataframes in `CapAnnDataDF`.
- **New Methods for Accessing Keys**: Added `obs_keys` and `var_keys` methods to `CapAnnData` for retrieving column keys without load content of `.h5ad` file to memory.
- **Append columns from disc**: Added the possibility to join the new column from disc to in-memory DataFrame. Previously, it was only possible to read new DataFrame from disc inplace of in-memory one.
- **DataFrame Setters**: Added validation in DataFrame setters to ensure correct data types and shapes.

Changed

- **Refactored CapAnnData Class**:
- Moved `RawLayer` to a separate class.
- Introduced `BaseLayerMatrixAndDf` as a base class for `CapAnnData` and `RawLayer`.
- Simplified `read_obs`, `read_var`, and `overwrite` methods.
- Enhanced `_read_df` to handle column order and in-memory DataFrame updates.
- Replaced `read_obs` and `read_var` methods to support resetting DataFrames and incremental reads.

Fixed

- **Empty Column Order Handling**: Fixed issue with empty column order attribute in `CapAnnDataDF`.
- **Overwrite Method**: Corrected handling of column order in the `overwrite` method to avoid type mismatches.

Removed

- **Context Manager for AnnData Files**: Removed context manager method `read_anndata_file` from `CapAnnData`.

Fixed
- Bug in `overwrite` method for empty `obs`/`var` sections by ensuring that the `column_order` attribute is always of type `object`.

Added
- Initial release of CAP-AnnData.
- Introduced the `CapAnnData` class for managing AnnData files, with functionalities to:
- Read and write specific columns of `obs` and `var`.
- Handle the `X` and `raw.X` matrices efficiently.
- Link and manage `obsm` and `uns` sections lazily, loading them only when accessed.
- Included the `CapAnnDataDF` class to extend `pandas.DataFrame` for handling partial reads and writes, with additional methods for renaming and removing columns.
- Provided the `CapAnnDataUns` class to manage the `uns` section of AnnData files, tracking keys to remove upon overwrite.
- Implemented methods to facilitate in-memory modifications and saving changes back to the file, including the `overwrite` method to selectively update sections of the AnnData file.