Add unit conversion to `DU` to recipes that use `toz`

[schlunma]

Description

Adapts recipes that use toz in light of https://github.com/ESMValGroup/ESMValCore/pull/2509.

Requires

• https://github.com/ESMValGroup/ESMValCore/pull/2509
• https://github.com/ESMValGroup/ESMValCore/pull/2560
• https://github.com/ESMValGroup/ESMValCore/issues/2559

Note: There are two example recipes that use toz for which we don't need to change anything since they don't have a diagnostic:

• https://github.com/ESMValGroup/ESMValTool/blob/main/esmvaltool/recipes/examples/recipe_check_obs.yml
• https://github.com/ESMValGroup/ESMValTool/blob/main/esmvaltool/recipes/examples/recipe_preprocessor_derive_test.yml

https://github.com/ESMValGroup/ESMValTool/blob/main/esmvaltool/recipes/examples/recipe_check_obs.yml

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• [ ] 🧪 Recipe runs successfully
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