refactor: 🐎 ShowcaseView optimization

[Sahil-Simform]

Description

• Optimized Overlay performance by eliminating unnecessary rebuilds and update calls.
• Enhanced documentation for better clarity and ease of use.
• Improved clipper functionality and optimized custom painting to boost rendering efficiency.
• Fixed memory leaks by removing unused widgets that were still attached to the widget tree.

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

None