fix(avatar): correct grid rendering for odd sizes and eliminate extra margins (#12)

[MuhammadSaim]

This PR resolves Issue #12 which affects avatar rendering when using high or odd gridSize values.

Problem

• For odd gridSize values (e.g., 9), the center column is skipped during mirroring, causing asymmetry.
• For larger even grid sizes (e.g., 10), there's a small margin or padding on the right and bottom of the image.

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What’s Changed

• Added support for drawing the center column when gridSize is odd
• Improved drawPixel logic to clamp within image bounds
• Ensured the avatar fills the image completely without leaving empty margins