Diagnostics: Tropopause pressure, temperature, height and icao height

This ticket was created to explore the AI Code gen workflow.

Migrate the tropopause diagnostics of pressure, temperature, height and icao height from UM to LFRic.
The UM code can be found in _atmosphere/PWS_diagnostics/pws_tropoht_mod.F90_.

Notes for Claude since our first attempt:
- The UM has updated the maximum tropopause height permitted in the operational UM code from 22km to 32km, and this must be reflected in LFRic.
- Ignore the existing LFRic code which searches from tropopause using a different approach. We want to reproduce the UM logic.

My latest _claude.md_ should now ensure that any code review will compare the new kernel logic against the original UM logic.

Start with _atmosphere/PWS_diagnostics/pws_tropoht_mod.F90_ and trace the UM logic for tropopause pressure, temperature, height and ICAO height. Compare the resulting kernel logic against the original UM behavior, including the updated 32 km maximum, and verify that all four diagnostics are reproduced in LFRic.

Written by the indexing model from the issue text.