fix(ml): stabilize MIGraphX inference (#28444)

* fix: stabilize ROCm MIGraphX inference

Serialize MIGraphX session runs so lazy compiles cannot overlap within a worker.

Use a fixed face-recognition batch size for MIGraphX to avoid compiling a new program for each detected face count.

* fix(ml): increase ROCm worker timeout

* fix(ml): narrow MIGraphX compile locking

* docs: format environment variables table

* docs: apply prettier to environment variables table