Handle Type Coercion Rules (e.g. int + float = float)

Implement type coercion rules for binary operations.

Requirements:

• Define type hierarchy and coercion rules
• Implement common type finder (int + float = float)
• Apply widening conversions (int → float, char → int)
• Detect narrowing conversions (float → int) with warnings
• Handle mixed-type expressions
• Test coercion with various type combinations
• Report dangerous coercions