* Add BMIS number support for business customer rates
Introduces a new `bmisNumber` option to journey requests, allowing bahn.business customers to access corporate rates by providing their 7-digit BMIS number. Adds documentation and a `createBusinessClient` helper for convenience. The request payload now includes a `firmenZugehoerigkeit` object when a BMIS number is set.
* Update cspell.config.json
Update cspell.config.json to fix spell check issues in PR #30
* allow value -1 for transfers option in journeys() for db and dbnav profiles
* add unit test for implicitly unconstrained transfers
* implement `formatTransfers()`, use it `formatJourneysReq()` functions and re-add corresponding unit test