Allows specifying an environment variable to only be applied to the
child, e.g.:
    ./measure_startup_oh -e LD_PRELOAD=libsmctrl.so
Or for starting the child process via a intermediate task, e.g.:
    ./measure_startup_oh ./nvtaskset 0xf ./measure_launch_oh 1

This allows for correctly measuring the startup overhead in the
evaluation of the ECRTS'25 partitioning paper.

This change better aligns gpu-microbench with the assumptions of
the cuda_scheduling_examiner Makefile.

Supports ECRTS'25 partitioning paper.

To nicely parse the resultant output, one could use the following
shell pipeline:

./measure_startup_oh 2>&1 | cut -d "=" -s -f 2 | cut -d " " -f 2 \
                          | tr "\n" " " | sed 's/$/r - p/' | dc

This is to reduce the impact of scheduling noise when measuring a
very large number of samples.

This change is to support the ECRTS'25 partitioning paper.

=> Uploads a large texture to the GPU on every frame
=> Requires the freeglut library (freeglut3-dev on Ubuntu)
=> Due to special requirements, not built by default
=> Written for Anderson and Bakita RTAS'24 paper

Benchmark supports:
=> Warms up the GPU and kernel code before sampling
=> Uses a flag in zero-copy memory to track when a kernel begins
=> Outputs summary statistics to stderr, and sample data to stdout

- Add a more reliable heuristic for how long to run the CPU-side
  copy monitor.
- Check that copies sizes are appropriately divisible.
- Fix parsing issue for copies larger than 8192 GiB.
- Clean up, and document bugs in, the time synchronization code.
- Wait for user before logging copies.