cabana: enhance message heatmap visualization

[deanlee]

This update improves the visualization of the message heatmap by enhancing the calculation of alpha transparency for bits with flips. Key changes include:

• Improved visibility for small bit flips: A minimum alpha value ensures that bits with few changes remain visible, helping users detect subtle patterns more easily.
• Logarithmic scaling refinement: The alpha transparency now better reflects variations in bit flip counts, providing more accurate visual scaling of changes.
• More precise scaling based on maximum bit flips: Alpha values are now determined by the maximum bit flip count, rather than the total message count, improving clarity for both high and low-frequency flips across messages.

These enhancements provide a more intuitive and visually accurate representation of bit changes, making it easier to detect patterns and boundaries in the heatmap for better analysis.

Example: WEEL_SPEEDS Message

Before	After

Actual DBC Message: