Add customizable snake and knight animation increments

[Michal-Szczepaniak]

Make snake and knight animation's increments customizable.

Description

In my keyboard i'm using ring rgblight which causes snake and knight animations to go in circle instead from left to right. While I changed led map
#define RGBLIGHT_LED_MAP { 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 3, 1 }
its not enough because now the animation is stuttering because it lights up one led on top and in second cycle on bottom. The goal is to make it light up both on top and bottom. This achieves said goal but also makes animation 2x faster.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[stale]

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