Speedup environment activation, part 2 (#25633)

This is a direct followup to #13557 which caches additional attributes that were added in #24095 that are expensive to compute. I had to reopen #25556 in another PR to invalidate the GitLab CI cache, but see #25556 for prior discussion.

### Before

```console
$ time spack env activate .

real	2m13.037s
user	1m25.584s
sys	0m43.654s
$ time spack env view regenerate
==> Updating view at /Users/Adam/.spack/.spack-env/view

real	16m3.541s
user	10m28.892s
sys	4m57.816s
$ time spack env deactivate

real	2m30.974s
user	1m38.090s
sys	0m49.781s
```

### After
```console
$ time spack env activate .

real	0m8.937s
user	0m7.323s
sys	0m1.074s
$ time spack env view regenerate
==> Updating view at /Users/Adam/.spack/.spack-env/view

real	2m22.024s
user	1m44.739s
sys	0m30.717s
$ time spack env deactivate

real	0m10.398s
user	0m8.414s
sys	0m1.630s
```

Fixes #25555
Fixes #25541 

* Speedup environment activation, part 2
* Only query distutils a single time
* Fix KeyError bug
* Make vermin happy
* Manual memoize
* Add comment on cross-compiling
* Use platform-specific include directory
* Fix multiple bugs
* Fix python_inc discrepancy
* Fix import tests

var/spack/repos/builtin/packages/clingo/package.py

@@ -66,7 +66,8 @@ def cmake_python_hints(self):
         current spec is the one found by CMake find_package(Python, ...)
         """
         python_spec = self.spec['python']
-        include_dir = python_spec.package.get_python_inc()
+        include_dir = join_path(
+            python_spec.prefix, python_spec.package.config_vars['python_inc']['false'])
         return [
             self.define('Python_EXECUTABLE', str(python_spec.command)),
             self.define('Python_INCLUDE_DIR', include_dir)