Handle station actions and data payloads

[Wheemer]

Summary

• allow actions to target station entities as well as child devices
• centralize desired-state payload construction for sync and async clients
• include action data payloads in addition to extra fields
• use UTC payload timestamps, omit child deviceSN for station-level actions, and return the shadow update response from action helpers

Validation

• Parsed all xsense Python files with AST
• Ran git diff --check