Add country Mexico (MX)

The following list of holidays needs to be verified/completed:
|Date | Flags | Name|
| --- | --- | --- |
| 01-01 | [NF] | Año Nuevo |
| 05-01 | [NF] | Día del Trabajo |
| 09-16 | [NF] | Día de la Independencia |
| 12-12 | [NRF] | Nuestra Señora de Guadalupe |
| 12-25 | [NRF] | Navidad |
| | [NV] | Día de la Constitución |
| | [NV] | Natalicio de Benito Juárez |
| | [NRV] | Jueves Santo |
| | [NRV] | Viernes Santo |
| | [NV] | Día de la Revolución |

Checklist:
* What type is the easter date?
- [ ] orthodox
- [x] western
- [ ] All holidays (i.e. days "which are defined by law on which business or work are suspended or reduced") are listed
- [ ] Legal sources which define the holidays are provided
- [ ] The spelling of the holiday names is correct
- [ ] The given dates (independent of year) of the holidays are correct

Start by reviewing existing country holiday entries and the repository’s tests or data-generation entry points; this issue names no specific file. Verify Mexico’s listed holidays, dates, spelling, legal sources, and Western Easter classification, then add the completed Mexico (MX) entry and confirm the relevant checks pass.

Written by the indexing model from the issue text.