节假日日历

A holiday calendar extension that automatically updates holidays from 2018 onward, based on https://github.com/gyxing/calendar.crx Added timeout handling for API requests and cache checks. Changed the holiday update rules to allow early attempts to retrieve the next year's holidays, such as those for 2020. Fixed a bug in the number of days in a month. Added week number display. Automatically updates holidays for 2021 and later; modified from https://github.com/gyxing/calendar.crx Removed the jQuery dependency, fixed an issue where next year's holiday information could not be retrieved when a local cache existed, and fixed a nonfunctional dropdown.