Replace magic number with GRASS_PATTERN_WIDTH constant

[Copilot]

Addresses feedback to replace the magic number 8 in the grass pattern rendering code with a named constant for clarity.

Changes

• Added GRASS_PATTERN_WIDTH = 8 constant with descriptive comment
• Replaced hardcoded 8 values in grass pattern loop with the constant

# Before
for i in range(0, WIDTH, 8):
    offset = (state["scroll_offset"] + i) % 8

# After
for i in range(0, WIDTH, GRASS_PATTERN_WIDTH):
    offset = (state["scroll_offset"] + i) % GRASS_PATTERN_WIDTH

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[atarukun]

LGTM

[Copilot]

Pull Request Overview

This PR refactors the grass pattern drawing code by extracting the magic number 8 into a named constant GRASS_PATTERN_WIDTH. This improves code maintainability by making the purpose of the value clear and centralizing its definition.

Key Changes:

• Added GRASS_PATTERN_WIDTH = 8 constant definition
• Replaced hardcoded 8 values in grass pattern loop with the new constant

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