Spec #38.5: Implement 2D array support

[treytomes]

Description

Extend array support to two-dimensional arrays: DIM M(rows, cols), M(i,j) access and assignment.

ECMA-55 References

• ECMA55-ARR-008: 2D array declaration
• ECMA55-ARR-009: 2D subscript syntax
• ECMA55-VAR-012: Bounds checking both dimensions

Acceptance Criteria

• Parse DIM A(m,n) for 2D arrays
• Bounds respect BASE for both dimensions
• Access M(i,j) in expressions
• Assignment LET M(i,j) = value
• Bounds checking for both subscripts
• Mix of 1D and 2D arrays works correctly
• All tests pass
• Test coverage ≥ 80%

Parent Issue

Part of #38 - Implement DIM and OPTION BASE for array support

Estimated Effort

3-4 hours

Dependencies

Depends on Spec #38.4 (1D array assignment)