restore executor-based spinning in opennav_docking

[bkoensgen]

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	N/A
Primary OS tested on	Ubuntu 24.04
Robotic platform tested on	N/A
Does this PR contain AI generated software?	No
Was this PR description generated by AI software?	No

---

Description of contribution

• Restore the executor-based spinning for docking tests that Replace rclcpp::spin_some and rclcpp::spin_all #5521 introduced so we keep the executor driving callbacks instead of rclcpp::spin_some.
• Update the detector-focused unit tests added in feat(opennav_docking): add on-demand detector client & unit tests for dock plugins (#5015) #5218 to follow the same executor pattern for consistent coverage.