fix(plugins/isocalendar): algorithm improvements for date ranges

[lowlighter]

Closes #753
Relates to #598

• This removes the "padding" trick to just force the starting date on a sunday (day 0 in JS)
• It also forces the time to be set at 00:00:00.000 for starting ranges and 23:59:59.999 for ending ranges, rather than keeping the current time, which could causes some days to be misreported
• Calendar are now fetched 4 weeks (28 days) at a time to avoid API timeouts for large users
• Merged the fetching between isocalendar and other statistics to avoid duplicate calls

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• todo: retest in a few day to ensure sunday logic is working