Operation request: Base26

## Summary

The Base26 as an Operator convert integer to string, or vice versa.
With an option with a recommended setting for math (A=0, AA=00, Z=25, BA=26) or cryptographic (A=1, AA=27, Z=26, BA=53) purposes option.
And normal or reversed letter order option.

### Example Input

GCHQ AND CYBERCHEF

### Example Output

```bash
# math
# normal
107006 0341 610781823241
# reversed
286006 02366 1078456576966

# crypto
# normal
125285 1044 827961970400
# reversed
304285 3069 1295636724125
```

The issue names no files, tests, or entry points. First locate how CyberChef operations and their tests are organized, then define the Base26 options and conversion cases from the examples; done means the requested math and cryptographic modes, letter orders, and both conversion directions are covered.

Written by the indexing model from the issue text.