Remove duplicate j < 0 boundary check in dig validation

[Copilot]

Addresses review feedback about redundant boundary checking in _check_dig_fits_inside. The condition j < 0 was checked twice: first at line 317, then again in the compound condition at line 321.

Changes:

• Removed redundant j < 0 from compound condition, keeping only j + self.thick - 1 >= shape[1]

# Before
if j < 0:
    raise DigOutsideShape(...)
if j < 0 or j + self.thick - 1 >= shape[1]:  # j < 0 already checked above
    raise DigOutsideShape(...)

# After
if j < 0:
    raise DigOutsideShape(...)
if j + self.thick - 1 >= shape[1]:
    raise DigOutsideShape(...)

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