Replace remaining calls to legacy `np.random.seed()`

Thanks for all of your work on TPOT! I and my colleagues use it very often for a variety of synthetic biology research projects.

I'd like to ask that TPOT 2 accept / use only [`np.random.Generator`](https://numpy.org/doc/stable/reference/random/generator.html) objects as an alternative to `int` RNG seeds, and avoid using the global / legacy `np.random` number generator, even internally, if possible. A quick search through the TPOT2 code at the time of writing (11/17/23), shows this is largely already the case except for 3 remaining instances of the string "random.seed", which refer to the legacy [`np.random.seed()`](https://numpy.org/doc/stable/reference/random/generated/numpy.random.seed.html).

Our code sometimes executes multiple `TPOTRegressors` in parallel, and TPOT 1's dependence on the global `np.random` generator has caused problems with repeatability. For example, if unpredictable OS-level thread scheduling changes the sequence of calls to the shared [`np.random.randint()`](https://numpy.org/doc/stable/reference/random/generated/numpy.random.randint.html) or similar functions. There are workarounds, e.g. using subprocesses instead of threads, but IMO TPOT should be maximally flexible and ideally not require workarounds.