Add type coercion for property assignments

[sergiobayona]

Related to #137

Issue #137 identified that integer properties coerce string values (e.g., "30" → 30). However, investigation reveals that no coercion is currently happening - values are stored as-is and validations incorrectly pass for mismatched types.

Current Behavior

class TestModel
  include EasyTalk::Model
  define_schema do
    property :name, String
    property :count, Integer
  end
end

model = TestModel.new(name: 30, count: "42")
model.name   # => 30 (Integer, not coerced to String)
model.count  # => "42" (String, not coerced to Integer)
model.valid? # => true (incorrectly passes!)

Proposed Coercions

Type	Input	Coerced Output
String	30 (Integer)	"30"
String	3.14 (Float)	"3.14"
String	:hello (Symbol)	"hello"
String	true/false	"true"/"false"
Integer	"42" (String)	42
Integer	42.9 (Float)	42 (truncate)
Float	"3.14" (String)	3.14
Float	42 (Integer)	42.0
BigDecimal	"123.45" (String)	BigDecimal("123.45")
BigDecimal	123.45 (Float)	BigDecimal("123.45")
T::Boolean	"true", "1", 1	true
T::Boolean	"false", "0", 0	false
Date	"2024-01-15" (String)	Date.parse("2024-01-15")
Time	"2024-01-15T10:30:00Z"	Time.parse(...)
DateTime	"2024-01-15T10:30:00Z"	DateTime.parse(...)
Symbol	"active" (String)	:active
Array	Single value	[value] (wrap in array)

Design Considerations

1. Fail on impossible coercion - "abc" → Integer should fail validation, not coerce to 0
2. Configurable - Add EasyTalk.configure { |c| c.coerce_types = true } (default: true for Pydantic-like behavior)
3. Coerce on assignment - Happens in the attribute writer, before validation
4. Respect nilable types - nil should pass through without coercion for T.nilable types

Implementation Notes

• Coercion should happen in EasyTalk::Model when defining attribute accessors
• Consider creating a TypeCoercer class with type-specific coercion logic
• Invalid coercions (e.g., "abc" to Integer) should leave value as-is and let validation fail