Math.log(0)/log2(0)/log10(0) return NaN instead of −∞ (Python/JS parity)

[aallan]

Surfaced by CodeRabbit's review of the #421 decomposition (#789). Pre-existing — the wrapper moved verbatim from codegen/api.py.

vera/runtime/math.py's _math_unary_host converts every ValueError from Python's math module into NaN, to mirror IEEE 754 / JS for genuine domain errors (e.g. log(-1) → NaN). But Python's math.log(0.0) raises ValueError (math domain error) at the pole, where IEEE 754 and JS Math.log(0) both give −∞. So Vera's Math.log(0) / log2(0) / log10(0) return NaN under the Python/wasmtime runtime while the browser/JS runtime returns −∞ — a parity violation.

Fix: special-case x == 0 → -inf in _math_unary_host for log/log2/log10, keeping the ValueError → NaN path for true domain errors. Add a tests/test_browser.py parity case for log(0).