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Bound Decimal rendering to ClickHouse precision limits (#271)

The adapter previously emitted Decimal64(scale) for every Decimal parameter regardless of value size and rendered the coefficient with Decimal.to_string/2 verbatim. Both the inline literal path (expr/4) and the parameter type path (param_type/1) are now guarded by a shared decimal_precision_and_scale!/1 helper that:

- rejects non-finite values (NaN, Infinity) with ArgumentError
- rejects scale > 76 with ArgumentError
- rejects coefficients with more than 76 digits with ArgumentError
- rejects computed precision > 76 with ArgumentError

param_type/1 now emits Decimal(precision, scale) sized to the actual value (up to ClickHouse's Decimal256 ceiling of precision 76) instead of always Decimal64(scale). Rendering goes through a new decimal_to_string/1 helper that, when the upstream Decimal library exposes Decimal.to_string/3 with :max_digits, caps output at 77 digits and otherwise falls back to Decimal.to_string/2.

Behavioral change for callers: Decimal parameters and inlined Decimal literals that exceed ClickHouse's Decimal limits, or that are NaN or Infinity, now raise ArgumentError at render time instead of silently producing malformed SQL. No new public option or API surface is added.

Co-authored-by: Eric Meadows-Jönsson <eric.meadows.jonsson@gmail.com>

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