nvproxy: expose CLOCK_MONOTONIC_RAW as a distinct clock for capProfiling

GPU profilers (Nsight Systems/CUPTI) build their trace timeline from
CLOCK_MONOTONIC_RAW. gVisor serves CLOCK_MONOTONIC_RAW as an alias of
CLOCK_MONOTONIC, this will drift from CLOCK_MONOTONIC_RAW breaking profiling.

When nvproxy is enabled with `capProfiling`, this change exposes
CLOCK_MONOTONIC_RAW as a clock distinct from CLOCK_MONOTONIC that tracks the
host's CLOCK_MONOTONIC_RAW (absolute, unadjusted). CLOCK_MONOTONIC is
unchanged. When profiling is disabled, CLOCK_MONOTONIC_RAW continues to alias
CLOCK_MONOTONIC as before.