fix(theme): update velvet theme to display Python environment correctly

[prathishpratt]

Updated the velvet theme configuration to use a Powerline style and fetch the virtual environment details accurately. Changed colors and adjusted the template for better readability and consistency.

Prerequisites

• I have read and understood the contributing guide.
• The commit message follows the conventional commits guidelines.
• Tests for the changes have been added (for bug fixes / features).
• Docs have been added/updated (for bug fixes / features).

Description

The velvet theme in oh-my-posh has been updated to:

1. Use a Powerline style for better visual alignment.
2. Fetch and display the Python virtual environment (Venv) accurately.
3. Enhance readability by modifying colors and adjusting the template.

This change improves user experience by clearly displaying the active Python environment in the terminal.

Before the change:

The right component for environment doesn't work properly.

Updated change looks like this:

[JanDeDobbeleer]

@prathishpratt we're not accepting changes to themes anymore, they merely act as examples which can be used, but tweaks need to done on your end.