Fix Swiss public transport initial data for attributes

[miaucl]

Proposed change

Fill attribute data at startup, instead of only after the first update triggered by the coordinator.

Discord dev_core: When using a coordinator using cloud_polling to load data for a platform and the platform treats its chunk of data provided by to coordinator in _handle_coordinator_update, I see following behaviour, that the platform gets setup quite fast, but the first time any data is provided to that platform through the coordinator, it takes 90s (update_interval). Even though using async_config_entry_first_refresh at the beginning. Is that normal or is there a way to trigger that faster? I find it a bit strange that one has to wait for 90s to get data after the integration config flow has ended.

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Hey there @fabaff, mind taking a look at this pull request as it has been labeled with an integration (swiss_public_transport) you are listed as a code owner for? Thanks!

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