Use environment variable to identify conda / mamba (#14515) Conda and mamba both set an environment variable which refers to the base environment's executable path, use that in preference to less reliable methods, but fall back on the other approaches if unable to locate the executable this way. Additionally, change the search to look for the bare command name rather than the command within the top level of the active environment, I'm dubious this approach works with any current conda / mamba version which usually place their executable links in a `condabin` directory or elsewhere not at the same level as the Python executable. I believe this will also address https://github.com/ipython/ipython/issues/14350, which I'm also seeing in a Windows context where the regex fails to parse and causes a traceback.