[NumericalOperator] Addition, subtraction, multiplication and division: numpy backend (#61)

[ArthurPendragn]

[NumericalOperator] Addition, subtraction, multiplication and division: numpy backend (#61)

• New ops: ADD, SUBTRACT, MULTIPLY, DIVIDE added to NumericOpType + dispatch
• Binary extraction: BinOp(+, -, *, /) and CallOp(np.add, np.subtract, np.multiply, np.divide) canonicalize to typed NumericOp with a constant and a reversed flag
• reversed flag: tracks operand order for asymmetric ops (e.g. 3 - df, 12 / df)
• Guard against var-op-var: _is_binary_extractable ensures extraction is skipped when both args are DataOp placeholders
• New tests: process, extraction, round-trip correctness, and var-var guard for all four ops

Closes #61

[codecov]

Codecov Report

❌ Patch coverage is 75.67568% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
stratum/optimizer/ir/_numeric_ops.py	73.52%	11 Missing and 7 partials ⚠️

Flag	Coverage Δ
unittests	91.73% <75.67%> (-0.60%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
stratum/optimizer/ir/_ops.py	98.26% <100.00%> (-0.25%)	⬇️
stratum/runtime/_object_size.py	100.00% <100.00%> (ø)
stratum/optimizer/ir/_numeric_ops.py	84.28% <73.52%> (-10.66%)	⬇️

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[e-strauss]

@ArthurPendragn thanks for the implementation of these binary operators. I merged in your commit together with another commit which adds support for var-op-var , which eliminates the need for the guard and increases the code coverage.