fix(restheadspec,resolvespec): stop casting SqlNull-wrapped and citext columns to TEXT in filters

reflect.Type.Kind() on spectypes.SqlNull[T] wrappers (SqlInt16/32/64,
SqlFloat64, SqlBool, SqlString, and embedders like SqlTimeStamp) always
reports reflect.Struct, never the wrapped T. ValidateAndAdjustFilterForColumnType
treated those as "complex" columns and forced CAST(col AS TEXT) on eq/gt/lt
filters, e.g. CAST(atdetail.rid_parent AS TEXT) = '90446096', which can't
use the index on rid_parent.

Add spectypes.UnwrapKind to see through SqlNull wrappers to the underlying
Kind, and use it in GetColumnTypeFromModel so numeric/string SqlNull columns
are recognized correctly and compared natively.

Also stop unconditionally casting to TEXT for LIKE/ILIKE and add
reflection.IsCitextColumn: citext columns are already case-insensitive, so
casting them to TEXT flips to case-sensitive matching and defeats a citext
index.

pkg/reflection/model_utils.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/bitechdev/ResolveSpec/pkg/modelregistry"
+	"github.com/bitechdev/ResolveSpec/pkg/spectypes"
 )
 
 type PrimaryKeyNameProvider interface {
@@ -728,19 +729,19 @@ func GetColumnTypeFromModel(model interface{}, colName string) reflect.Kind {
 			// Parse JSON tag (format: "name,omitempty")
 			parts := strings.Split(jsonTag, ",")
 			if parts[0] == sourceColName {
-				return field.Type.Kind()
+				return spectypes.UnwrapKind(field.Type)
 			}
 		}
 
 		// Check field name (case-insensitive)
 		if strings.EqualFold(field.Name, sourceColName) {
-			return field.Type.Kind()
+			return spectypes.UnwrapKind(field.Type)
 		}
 
 		// Check snake_case conversion
 		snakeCaseName := ToSnakeCase(field.Name)
 		if snakeCaseName == sourceColName {
-			return field.Type.Kind()
+			return spectypes.UnwrapKind(field.Type)
 		}
 	}