Python: add fdsplotlib to fds_python_env

[rmcdermo]

With this change, you can rebuild your python environment per these instructions and then import fdsplotlib from anywhere if the fds_python_env is activated:

(fds_python_env) fds (master) $ ipython
Python 3.12.9 (main, Feb  4 2025, 14:38:38) [Clang 16.0.0 (clang-1600.0.26.6)]
Type 'copyright', 'credits' or 'license' for more information
IPython 9.5.0 -- An enhanced Interactive Python. Type '?' for help.
Tip: Use `%timeit` or `%%timeit`, and the  `-r`, `-n`, and `-o` options to easily profile your code.

In [1]: import fdsplotlib

In [2]: