1c57be5c44
Replaces manual isinstance/<=0 checks in calculate_spread_ratio() and determine_order_limits() with _valid_tick_price(), ensuring NaN, inf, -inf, zero, negative, bool, and invalid-string tick values are consistently rejected across all trading helpers. Adds regression tests covering numeric-string acceptance and every invalid-value category for both functions. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>