Lazy load CondaPkg (and Pkg), I think LazyModules for that, or better option?

At least when I set:
ENV["JULIA_CONDAPKG_BACKEND"] = "Null"

I get: ERROR: InitError: CondaPkg is using the Null backend but Python is not installed

though, so not investigating further (I have Python installed).

With this one loads but not any faster (but should too):
```
ENV["JULIA_PYTHONCALL_EXE"] = "@PyCall" # optional

julia> ENV["JULIA_PYTHONCALL_EXE"] ="/usr/local/bin/python3";

julia> @time using PythonCall
┌ Warning: Python library "/usr/local/lib/python3.12/config-3.12-x86_64-linux-gnu/libpython3.12.a" could not be opened.
└ @ PythonCall.C ~/.julia/dev/PythonCall/src/C/context.jl:122
┌ Warning: Python library "/usr/local/lib/libpython3.12.a" could not be opened.
└ @ PythonCall.C ~/.julia/dev/PythonCall/src/C/context.jl:122
ERROR: InitError: Could not find Python library for Python executable "/usr/local/bin/python3".

If you know where the library is, set environment variable 'JULIA_PYTHONCALL_LIB' to its path.
```

Start by reproducing the CondaPkg Null-backend error and the PythonCall initialization failure described in the issue, then inspect how CondaPkg and Pkg are loaded. The referenced warning originates at ~/.julia/dev/PythonCall/src/C/context.jl:122; done should mean startup no longer eagerly loads these dependencies while the configured Python backends still initialize correctly.

索引モデルが issue の本文から書いたものです。