Why

Enable all the disabled RET rules and fixed all the issues.

Closes #2192

What changed

• Removed all the disabled RET related rules from the pyproject.toml. So, all the RET related checks are done with ruff check.

Checklist

• Tests added/updated
• Changelog entry added (uv run towncrier create ...)
• External docs updated (if user-facing or ops-facing change)
• Internal .md docs updated (internal knowledge and AI code tools knowledge)
• I have reviewed AI generated content

Summary by cubic

Activates RET return rules in ruff and resolves RET504 violations by returning values directly across the codebase. No behavior changes expected; adds a clear error when get_path_value receives an unsupported schema path. Aligns with #2192.

• Refactors
  • Removed disabled RET rules in pyproject.toml; ruff check now enforces them.
  • Replaced temporary variables with direct returns across auth, migrations, nodes/relationships, Git, GraphQL, tasks, events, telemetry, message bus, webhooks, server, and tests.
  • Added a ValueError for unsupported schema paths in node get_path_value.
  • No API, schema, or runtime behavior changes; tests updated only for style.

^{Written for commit 16f2659. Summary will update on new commits. Review in cubic}