Upgrade Composer dependencies

[ohmyfelix]

Summary

• Upgrade Composer constraints for Dependabot updates: contributte/nella ^0.3, contributte/phpstan ^0.3, contributte/tester ^0.4
• Refresh composer.lock including required transitive dependency updates
• Consolidates Dependabot PRs Bump contributte/nella from 0.2.0 to 0.3.0 #2, Bump contributte/tester from 0.3.0 to 0.4.1 #3, and Bump contributte/phpstan from 0.1.0 to 0.3.1 #4

Verification

• composer validate --strict
• make tests
• make phpstan
• make cs