fix: implement threshold-based FAB position validation

[zeeshanahmad0201]

Fixes #87

The previous implementation used exact integer comparison which was too strict for real-world scenarios. This change introduces a threshold-based approach that:

• Uses 10% of the navigation bar width as tolerance
• Better handles floating-point precision
• Maintains proper alignment validation
• Provides more reliable position detection

Changes made:

• Replaced integer comparison with double values
• Added threshold calculation (10% of width)
• Updated validation logic to use distance-based checks
• Maintained original validation intent while being more practical

Test Cases:

• Centered FAB with GapLocation.center now works properly
• End-positioned FAB with GapLocation.end continues to work
• Slight misalignments (within 10% threshold) are properly handled

Note: The previous fix in #23 was a step in the right direction but didn't fully resolve the position validation issues. This PR builds on that work to provide a more robust solution.