Add test for partially numeric spin option

[jdeguzman11]

Adds regression coverage for partially numeric spin option values such as 12abc.

The existing invalid option tests cover non-numeric, negative, and out-of-range values, but not values that begin with valid digits and contain trailing non-numeric characters.

Validation:

• python3 -m py_compile tests/instrumented.py
• python3 tests/instrumented.py src/stockfish
• 74 tests passed, 0 failed

No functional change.

[vondele]

I'm not so sure we want to test this works. This is largely undefined behavior / invalid input?

[jdeguzman11]

I'm not so sure we want to test this works. This is largely undefined behavior / invalid input?

That makes sense. My thought was to add regression coverage for the stricter numeric parsing added recently, specifically to ensure partially numeric values like 12abc continue to be rejected rather than partially parsed. But I agree that if malformed setoption input is considered outside the behavior Stockfish intends to guarantee, then this test may be too specific. Happy to drop or adjust it if there’s a more appropriate edge case to cover.