feat(bun): 🎉 Enhance nullability handling in column parsing

* Introduce explicit nullability markers in column tags.
* Update logic to infer nullability based on Go types when no markers are present.
* Ensure correct tags are generated for nullable and non-nullable fields.

pkg/writers/bun/type_mapper.go

@@ -192,8 +192,11 @@ func (tm *TypeMapper) BuildBunTag(column *models.Column, table *models.Table) st
 	}
 
 	// Nullable (Bun uses nullzero for nullable fields)
+	// and notnull tag for explicitly non-nullable fields
 	if !column.NotNull && !column.IsPrimaryKey {
 		parts = append(parts, "nullzero")
+	} else if column.NotNull && !column.IsPrimaryKey {
+		parts = append(parts, "notnull")
 	}
 
 	// Check for indexes (unique indexes should be added to tag)