Building boost.Python fails with non-standard Python installation on Windows

I'm able to successfully build boost.Python on my local machine with Python 3.13 using b2 like so:
```
.\bootstrap.bat vc143
.\b2 python=3.13 # other arguments
```

The issues start happening when I try to build on our Azure DevOps build agents. Because of _.\*\~reasons\~\*._ I can't install Python 3.13 directly on those build agents. So, I zipped up a python 3.13 installation, and in the build pipeline I grab the Python zip file and extract it to some directory, say, `Z:\Python313`. Then I created a user-config.jam in the root of the boost directory like the following:

```
using python : 3.13 : Z:\Python313 ;
```

And in the build pipeline, I try to build boost.Python like so

```
bootstrap.bat vc143 --with-python=3.13
b2 python=3.13
```

While bootstrap.bat succeeds, b2 fails with the following error:
```
error: "3.13" is not a known value of feature
error: legal values: "3.9"
```

So I understand that the way I'm trying to do this is a little bit unusual, but is there a way that I can get this to work? Or must Python be installed via the installer (because b2 uses `py` or the registry entries that the installer creates) to build boost.Python on Windows?

Start with the user-config.jam configuration and the bootstrap.bat and b2 entry points used in the report. Reproduce the Windows build with Python 3.13 extracted to Z:\Python313, then determine why b2 only recognizes Python 3.9. Done means the configured non-standard Python installation is recognized and Boost.Python builds successfully.

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