Update models.md, NULL values, typo or changed struct

[burner-account]

First: Thanks for the awesome lib!

sql.NullBool has a different internal structure

NullBool.Value is the Valuer interface func, not the storage.

// NullBool represents a bool that may be null.
// NullBool implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullBool struct {
	Bool  bool
	Valid bool // Valid is true if Bool is not NULL
}
``