Optimiser more 'L-centric' - minor modifications (#504)

* Update optimizers.py
* Update lightning_module.py

Fix persistence error calculation to handle dropped values in pv data (…

…#494)

* Fix persistence error calculation to handle dropped values in site data

* Fixed: To use >= 0 instead of != -1 for valid mask

* Update batch key from target_key to generation

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Co-authored-by: Alexandra Udaltsova <43303448+AUdaltsova@users.noreply.github.com>

Reduce test data size (#503)

Fix backwards compatibility for site encoder (#499)

Generalised data sampler support (#496)

#minor

improve uk backtest script (#497)

Python version ci hotfix (#495)

Train related tests (#491)

remove sample and replace with utils (#493)

#minor

Update coment in trainer config (#492)