feat: add cumulative extension cap (72h max) to extend_for_dispute

[Hassanmovic98]

Closes #710

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Description

Adds cumulative extension cap enforcement to the extend_for_dispute function. Markets can now extend deadlines for disputes, but total extensions are capped at 72 hours to prevent indefinite deadline extensions.

Changes

• Modified extend_for_dispute() to return Result<(), Error>
• Tracks cumulative extension hours in Market struct
• Enforces maximum 72-hour cap before allowing new extensions
• Returns ExtensionCapExceeded error when cap is exceeded

Type of Change

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

Testing

Contract compiles successfully with no errors.

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