Abstract theming to support custom themes

As a developer 
I want the package to support custom MUI themes and work with different versions of MUI (e.g., 5 and 6) 
so that I can seamlessly integrate it into my application without dependency conflicts.

Background:

The current implementation tightly couples the package with specific versions of @mui/material and @emotion, due to the use of createTheme and a predefined theme setup. This dependency constraint makes it challenging to use the package in applications with different MUI versions or custom themes. Refactoring the theming logic to be more abstract and flexible will enhance the package's utility and compatibility.

Acceptance Criteria:

• The package allows users to provide their own MUI theme configurations.
• The package works with at least MUI versions 5 and 6.
• Default theme behavior remains available but optional for users who do not provide custom themes.
• Updates to the README include guidance on how to integrate a custom theme.