Transaction Request URL Params

The TransactionRequestURLParams input dictionary accepted by encode_url contains:

Field	Type	Required	Meaning
`link`	`str`	Yes	Absolute HTTPS merchant endpoint without credentials or a fragment.
`label`	`str`	No	Human-readable source of the request.
`message`	`str`	No	Human-readable request description.

parse_url returns an immutable TransactionRequestURL dataclass with the same three attributes; missing optional values are None.