[codex] Add networked dynamic PETC controller wrapper

[JohnneyLee]

Summary

Adds a networked-control wrapper for sampled, delayed, event-triggered observations. The wrapper lets existing safe-control-gym controllers run behind bounded-delay communication channels without changing their controller API.

What changed

• Added safe_control_gym.controllers.networked with delay channels, static/dynamic PETC triggers, scheduling helpers, wrapper, and metrics.
• Added a standalone smoke example and a BaseExperiment integration example.
• Added a mobile robot MPC example showing dynamic PETC on path tracking with bounded observation delay.
• Added tests for FIFO delayed delivery, trigger behavior, and wrapper-held observations.
• Added docs/networked_control.md with usage, theory mapping, mobile robot MPC results, and before/after evaluation guidance.

Validation

Run locally in the Codex workspace:

python -m compileall safe-control-gym-networked-petc
5 lightweight test functions passed
python examples/networked_control/run_dynamic_petc.py --steps 80 --max-delay-steps 3
python examples/networked_control/run_mobile_robot_mpc_petc.py --steps 80 --max-delay-steps 4

Smoke output for the generic wrapper demo:

direct_rms_position: 1.2350
networked_rms_position: 1.3597
transmissions: 43
skips: 37
event_rate: 0.5375

Representative mobile robot MPC run:

Fresh MPC RMS tracking error: 0.0513 m
PETC MPC RMS tracking error: 0.0565 m
Transmissions: 75 / 260 samples
Event rate: 28.85%
Mean stale steps: 4.22
Max queue depth: 4

Notes

This PR does not claim closed-loop ISS for arbitrary tasks. It exposes practical network-state quantities such as update error, stale steps, queue depth, trigger margin, and eta so task-specific certificates can be layered on top.