fix(orders): reject prices that are not a multiple of the tick size

[cesarenaldi]

What

_resolve_price (limit orders) and _resolve_protected_market_price (market orders) validated prices by decimal-place count only. Decimal count matches tick-grid membership for power-of-ten ticks, but diverges on 0.005 and 0.0025 tick markets: a price like 0.007 has 3 decimals, passes validation, gets signed into the EIP-712 order, and is then rejected by the exchange. The client-side guard should fail fast instead.

Fixes #162.

How

Add a tick-grid membership check after the existing decimal-count check in both validators:

if price % tick_size != 0:
    raise UserInputError(f"price {price} must be a multiple of tick size {tick_size}.")

Purely additive: every previously valid price is a tick multiple and still passes; only off-grid prices that the exchange would reject anyway are now caught client-side.

Tests

• test_order_limit.py: parametrized on/off-grid cases for _resolve_price across 0.005, 0.0025, and 0.01 ticks including range boundaries, plus an end-to-end prepare_limit_order_draft test on a mocked 0.005 tick market.
• test_order_market.py: parametrized on/off-grid cases for _resolve_protected_market_price.

Verification

• uv run ruff format --check and uv run ruff check clean
• uv run pyright 0 errors
• uv run pytest tests/unit 1854 passed

Credit to @GiulioDER for the report and analysis in #162.

---

Note

Medium Risk
Stricter pre-sign validation changes which limit prices are accepted (no silent rounding) and affects EIP-712 order construction for tick sizes like 0.005/0.0025.

Overview
Introduces shared validate_price_on_tick_grid for limit price and market max_price / min_price, replacing duplicated _resolve_price and _resolve_protected_market_price logic.

Validation now enforces the allowed [tick, 1−tick] range, decimal precision derived from the tick (not RoundingConfig.price), and price % tick_size == 0 so off-grid values like 0.007 on a 0.005 tick fail client-side instead of being signed and rejected by the exchange. Valid prices are returned unchanged—limit order prep no longer round_normal-snaps user prices.

Unit coverage in test_order_context.py exercises on-grid acceptance, off-grid multiples, over-precision inputs, and out-of-range values across all supported ticks.

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