feat: Add support for Tibetan, Mongolian, and Bhutanese calendars

[hnw]

This pull request introduces support for calculating dates in the Tibetan lunar calendar and its derivative systems: the Mongolian and Bhutanese calendars.

Changes:

• Introduced @hnw/date-tibetan to handle date calculations for the Tibetan, Mongolian, and Bhutanese calendars.
• Added a new rule format for Tibetan calendar dates: (tibetan|mongolian|bhutanese) <cycle>-<year>-<month>-<leapmonth>-<day>-<leapday>.
• Added comprehensive unit tests for the new functionality. All tests are passing.

This enhancement expands the library's capability to support holidays for a wider range of countries.