📦 Migrate to phpstan v2 (max level), fix SA issues, PHP 8.4 deprecations

[andrew-demb]

… add phpstan-symfony, use max phpstan level, make phpstan happy

The last planned change before release the major version

[andrew-demb]

There's no more outdated dependencies except of psr/simple-cache (transitive)

$ composer outdated
Color legend:
- patch or minor release available - update recommended
- major release available - update possible

Direct dependencies required in composer.json:
Everything up to date

Transitive dependencies not required in composer.json:
psr/simple-cache 1.0.1 3.0.0 Common interfaces for simple caching

$ composer why psr/simple-cache
thecodingmachine/cache-utils v1.0.0 requires psr/simple-cache (^1)                 
thecodingmachine/graphqlite  v8.0.0 requires psr/simple-cache (^1.0.1 || ^2 || ^3) 

[Lappihuan]

looks good to me