Allow specifying exec_time_optimization_effort and memory_fitting_effort via CLI.

[golechwierowicz]

New compiler options (see title) have recently been exposed in JAX.

To use them users have to change their Python code like this:

jax.jit(f, compiler_options={
  "exec_time_optimization_effort": 0.5, # change here
 })

It would be very convenient to not modify the code but rely on CLI instead. For example:

JAX_EXEC_TIME_OPTIMIZATION_EFFORT=0.5 python3 jax_program.py