Fix /heartrate query parameters

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/heartrate endpoint has slightly different query paramaters, so here I make adjustment for that

Also, if timestamp includes timezone info, which is separated by +, e.g. 2024-04-07T07:22:48+00:00, then in url it is considered as space, so we need to escape it. That's exactly what urlencode does. BTW it is the same function that requests use for escaping characters as well

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@turing-complet Please review. Also, it is the last PR for now, so please make a release after that

[turing-complet]

Thanks, LGTM. I'll try to get a release out soon.