release: 3.1.0

2025-05-19 task(C/I): lint [Jonas Eberle] (46b09ad)
2025-05-19 feat(config): enable COA in inject() configuration [Jonas Eberle] (b512411)
2025-05-19 task(C/I): add tests for simple ContentObjects in inject() [Jonas Eberle] (4ee88b8)
2025-05-19 task(C/I): add a simple plain text test for inject() [Jonas Eberle] (646c092)
2025-05-19 task(C/I): use PHP8 attributes in phpunit tests [Jonas Eberle] (e0e208b)
2025-05-19 task(C/I): output deprecation warnings in phpunit [Jonas Eberle] (0b678a5)
2025-04-24 chore(style): use conventional commit style for release commit [Jonas Eberle] (4be529e)
2025-04-24 fix(README): update test status badges [Jonas Eberle] (d204ead)