feat: add arrow start offset option for improved arrow positioning

[DevArches]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.

Adds a new arrowStartOffset property to arrowOptions that controls how far from the center of the starting square an arrow begins, as a fraction of the square width. This allows developers to offset arrow origins toward the edge of the square for a cleaner look (similar to chess.com), where arrows emerge from the base of a piece rather than its center.

• 0 = arrow starts from the center of the square (default, preserves existing behavior)
• 0.3–0.4 = arrow starts near the edge of the square, giving a chess.com-like appearance
• 0.5 = arrow starts at the square boundary

Based on this issue #222

Fixes # (issue)

Type of change

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• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.

• Verified visually in Storybook ArrowOptions story with the new Start Offset slider across straight, diagonal, and knight move arrows
• Confirmed default value of 0 preserves existing arrow behavior
• pnpm test:static passes (tsc, eslint, prettier)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Screenshots (if appropriate):

Before:

After:

Additional context

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[DevArches]

Should be ready now. Just wanted to update some variable names and comments and then forgot to use prettier to format. This could be a nice improvement for my project that has some learning features like showing all possible moves a piece has. And since sometimes that can be in all directions, thats a lot of arrows covering up a piece.