Get 1.0.x linting pipeline steps to green

cspell is done.

phpstan I think we will need to approach in a couple of separate issues, starting on 📌 Adjust to propper dependency injection Active since it's already open.

Had to rerun the pipeline but we're good with this one. Merging so more work can be done on a new branch with a new MR but on the same fork as we do in the backport issue while we have this already in 1.0.x.

This is green on phpstan level 6 with a large baseline. I fixed the handful of errors that can't be baselined.

It was tempting to try to bring the baseline down further too but if we commit this as-is it will stop us making the baseline bigger, and then we can gradually reduce it over time.

Merged, just phpcs remaining :)

This is fixed now with 📌 Fix errors ignored in phpstan-baseline.neon Active as a phpstan follow-up.