Narrow RoundingNecessaryException for Money::of() with int amount

[simPod]

Summary

• Extends the zero-amount narrowing from Narrow RoundingNecessaryException for Money::of() with zero amount #13 to cover all integer amounts when the context doesn't involve step division
• When Money::of() is called with an int amount, scaling to higher precision just adds trailing zeros — no rounding needed
• Safe contexts: no context arg (default DefaultContext), new DefaultContext(), new AutoContext(), new CustomContext($scale), new CustomContext($scale, 1)
• CustomContext with step > 1 is still treated as potentially throwing (division by step can require rounding)

Fixes e.g. Money::of(500, 'USD', new CustomContext(4, 1)) being flagged as throwing RoundingNecessaryException.

Test plan

• Money::of(100, 'USD') — int + default context = no throw
• Money::of(100, $currency) — int + Currency instance = no throw
• Money::of(0, 'EUR', new CustomContext(4, 1)) — zero = no throw
• Money::of(0, $currency) — zero + safe currency = no throw
• Money::of(500, 'EUR', new CustomContext(4, 1)) — int + step 1 = no throw
• Money::of(500, 'EUR', new CustomContext(4)) — int + default step = no throw
• Money::of(500, 'EUR', new CustomContext(2, 5)) — int + step > 1 = may throw
• Money::of($string, 'EUR', new CustomContext(4, 1)) — string amount = may throw
• All existing tests pass