[REF] resource calendar (#24717)

Refactor resource calendar and resource mixin:
 - add a required timezone field on models 'resource.calendar' and 'resource.resource';
 - resource calendar attendances are now computed in the timezone of the resource
   or the calendar;
 - improve API of 'resource.calendar' and 'resource.mixin';
 - avoid other modules from using the implementation methods of 'resource.calendar';
 - refactor implementation of 'resource.calendar' to make it more efficient.