use scandir() in find_commands.py to avoid stat() calls against 23.7.x branch

[dholth]

Description

Fixes #13033, #13067

The original fix from PR #13035 is already in the main branch but not in the 23.7.x branch. This fix improves on #13035 by also removing the os.path.isfile() call.

In general, we should always use scandir(); I didn't notice any equally problematic listdir()/stat() pairs on a quick search through the conda source.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[dholth]

I tried this on wsl2. I installed miniconda3 including conda 23.5, and "conda info" was fast. I used conda to update itself, and conda startup was slow. I did not wait for it to finish starting. Then I checked out the main branch, and these fixes both against main or 23.7.x.

On the main branch with only the older fix conda was fast again. On my machine scandir() avoids 4 stat calls since there are 4 conda-* files in PATH.

This newer fix is not measurably different than the existing fix since it would only avoid 4 stat calls. But with scandir() it is still fast even if we call entry.is_file() before checking pat.match(entry.name). We should keep the current "match first" order to avoid following non-conda-* symlinks.

In the future we could even consider calling os.scandir(dir_path) without checking if not isdir(dir_path) first and catch FileNotFoundError / NotADirectoryError.

I also was able to run "conda content-trust" which AFAICT is not a new-style plugin in conda-content-trust=0.1.3 as installed in the test environment.