Add automatic type cast for integer literals

In parameterized statements integer literals, like Int(num), are replaced with a placeholders. For some expressions,
postgres interpreter will not have enough information to deduce the type. If this is the case postgres returns an error.
Int8, Int16, Int32.... functions now will add automatic type cast over a placeholder, so type deduction is always possible.

postgres/literal.go

@@ -6,35 +6,52 @@ import (
 	"github.com/go-jet/jet/v2/internal/jet"
 )
 
-// Bool creates new bool literal expression
-var Bool = jet.Bool
+func Bool(value bool) BoolExpression {
+	return CAST(jet.Bool(value)).AS_BOOL()
+}
 
 // Int is constructor for 64 bit signed integer expressions literals.
 var Int = jet.Int
 
 // Int8 is constructor for 8 bit signed integer expressions literals.
-var Int8 = jet.Int8
+func Int8(value int8) IntegerExpression {
+	return CAST(jet.Int8(value)).AS_SMALLINT()
+}
 
 // Int16 is constructor for 16 bit signed integer expressions literals.
-var Int16 = jet.Int16
+func Int16(value int16) IntegerExpression {
+	return CAST(jet.Int16(value)).AS_SMALLINT()
+}
 
 // Int32 is constructor for 32 bit signed integer expressions literals.
-var Int32 = jet.Int32
+func Int32(value int32) IntegerExpression {
+	return CAST(jet.Int32(value)).AS_INTEGER()
+}
 
 // Int64 is constructor for 64 bit signed integer expressions literals.
-var Int64 = jet.Int
+func Int64(value int64) IntegerExpression {
+	return CAST(jet.Int(value)).AS_BIGINT()
+}
 
 // Uint8 is constructor for 8 bit unsigned integer expressions literals.
-var Uint8 = jet.Uint8
+func Uint8(value uint8) IntegerExpression {
+	return CAST(jet.Uint8(value)).AS_SMALLINT()
+}
 
 // Uint16 is constructor for 16 bit unsigned integer expressions literals.
-var Uint16 = jet.Uint16
+func Uint16(value uint16) IntegerExpression {
+	return CAST(jet.Uint16(value)).AS_INTEGER()
+}
 
 // Uint32 is constructor for 32 bit unsigned integer expressions literals.
-var Uint32 = jet.Uint32
+func Uint32(value uint32) IntegerExpression {
+	return CAST(jet.Uint32(value)).AS_BIGINT()
+}
 
 // Uint64 is constructor for 64 bit unsigned integer expressions literals.
-var Uint64 = jet.Uint64
+func Uint64(value uint64) IntegerExpression {
+	return CAST(jet.Uint64(value)).AS_BIGINT()
+}
 
 // Float creates new float literal expression
 var Float = jet.Float