fix: MetaDrive sim on macOS (#33207)

[imperatormk]

Makes pytest tools/sim/tests/test_metadrive_bridge.py pass on macOS, no test changes. Fixes #33207. Requires commaai/metadrive#15 (without it the road is invisible to the model on macOS and the car won't drive).

Three points worked on:

• manager dies silently at startup: prepare() pre-imports the ui module (pyray -> Cocoa) inside the forkpty child, which aborts on macOS. Pre-importing only helps with fork start method, so skip it under spawn
• locationd rejects every cameraOdometry, so openpilot never engages: sim camerad's synthetic eof = frame_id * 0.05 is in a different clock domain than the IMU timestamps. Stamp eof from time.monotonic_ns()
• modeld only hits 13Hz on plain DEV=CPU, starving locationd. Use CPU:LLVM like everywhere else, with a probe fallback since libLLVM isn't guaranteed on macOS (afaik but safer anyway)

Verification

Verified on M1 Pro (macOS 27 beta)

[github-actions]

Process replay diff report

Replays driving segments through this PR and compares the behavior to master.
Please review any changes carefully to ensure they are expected.

✅ 0 changed, 66 passed, 0 errors