Fixes to config checks

[lchoquel]

• Fix check_is_initialized() used by tests and fix checking service agreement (now always global) for tests in client projects

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Summary by cubic

Fixes config initialization checks and switches service agreement validation to the global config. Tests now mirror runtime behavior and are reliable in client projects.

• Bug Fixes
  • check_is_initialized() resolves both core (CONFIG_NAME) and plxt.toml via config_manager.resolve_config_file and no longer calls init with a dry run.
  • Pytest plugin reads the service agreement from config_manager.global_config_dir (was pipelex_config_dir).
  • Tests updated to use the new resolution logic and create required config files.

^{Written for commit 1a30d03. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files