Revamp of Worksheet Class

- Refactored the Worksheet class to provide a more intuitive interface for accessing worksheet functionalities.
    * This includes the introduction of the `CellIndexer` class to make cell access more streamlined.

- Added exception handling across various methods to ensure safer operations when interacting with the worksheet.

- Introduced the `Cells` property to provide an intuitive way to access cells using their reference.
    * This encapsulates the cell accessing logic inside the `CellIndexer`, making the main `Worksheet` class less cluttered.

- Enhanced the `Name` property for worksheets to include better error handling.
    * This should prevent unexpected null references and provides clearer error messages.

- Extended image handling capabilities:
    * Added `AddImage` method, allowing users to easily insert images into the worksheet.
    * Enhanced `ExtractImages` to return a collection of Image objects rather than raw streams, improving usability.

- Implemented row and column dimension adjustments:
    * `SetRowHeight` and `SetColumnWidth` methods provide a way to customize row heights and column widths respectively.

- Added sheet protection functionality:
    * New methods `ProtectSheet`, `IsProtected`, and `UnprotectSheet` allow for setting, checking, and removing worksheet protection.

- Added utility methods and refactored some existing methods:
    * This includes methods for handling column letter indexing, image type determination, and cell/row creations.
    * Ensures that the main functionalities of the class remain clean and each method has a single responsibility.

- Enhanced merging cells capability with the `MergeCells` method.

- Added a method `GetSheetIndex` to retrieve the index of the current worksheet in the workbook.

Overall, these changes are aimed at making the `Worksheet` class more robust, user-friendly, and maintainable.

Author: Fahad Adeel