BEFORE:
the python derivation did not contain .nativeDrv and .crossDrv because
it was not from the __splicedPackages set
the python used in mk-python-derivation.nix was for host
```
nix-repl> pkgsCross.aarch64-multiplatform.python3Packages.xpybutil.nativeBuildInputs
[ «derivation /nix/store/bhz39ds4v02hn6x4py4mzjyilw4a589h-python3-aarch64-unknown-linux-gnu-3.10.7.drv» «derivation /nix/store/v880cnh4ml7czmivfbk3cdh93hz9yvbn-hook.drv» «derivation /nix/store/f243ab7wv92gqsmc9h7gr0qcnj0xcgdb-hook.drv» «derivation /nix/store/880lf8895bzn8d94lrr2y7ilgkxq0lc4-python-remove-tests-dir-hook.drv» «derivation /nix/store/fzjnhawfs1wpw58hcd1vxd9y750dc08y-python-remove-bin-bytecode-hook.drv» «derivation /nix/store/n8l59iparx98yfw8g5ydqmzmk3fdic75-setuptools-setup-hook.drv» «deri→
```
AFTER:
the python derivation does contain .nativeDrv and .crossDrv because
it is from the __splicedPackages set
those 2 are what makes nativeBuildInputs and buildInputs function
properly
the python used in mk-python-derivation.nix is for build
```
nix-repl> pkgsCross.aarch64-multiplatform.python3Packages.xpybutil.nativeBuildInputs
[ «derivation /nix/store/hvb9yxgv1133cfhxxd869sibldvv2vdx-python3-3.10.7.drv» «derivation /nix/store/v880cnh4ml7czmivfbk3cdh93hz9yvbn-hook.drv» «derivation /nix/store/f243ab7wv92gqsmc9h7gr0qcnj0xcgdb-hook.drv» «derivation /nix/store/880lf8895bzn8d94lrr2y7ilgkxq0lc4-python-remove-tests-dir-hook.drv» «derivation /nix/store/fzjnhawfs1wpw58hcd1vxd9y750dc08y-python-remove-bin-bytecode-hook.drv» «derivation /nix/store/n8l59iparx98yfw8g5ydqmzmk3fdic75-setuptools-setup-hook.drv» «derivation /nix/store/7vyhynla→
```
Python package sets can be overridden by overriding an interpreter
and passing in `packageOverrides = self: super: {...};`. This is fine
in case you need a single interpreter, however, it does not help you
when you want to override all sets.
With this change it is possible to override all sets at once by
appending a list of "extensions" to `pythonPackagesExtensions`.
From reading the implementation you might wonder why a list is used, and
not
`lib.composeExtensions`? The reason is the latter requires knowledge of
the library function. This approach should be easier for most users
as it is similar to how we append to lists of e.g. inputs or patches
when overriding a derivation.
Every package should have a maintainer and we should not throw it away if we arleady have one.
Also in reality the maintainer of python3 is also the one of python3-minimal
This simplifies usages and makes the default value consistent.
In a few cases, the default value was interpreted to be `false`,
but this is useless, because virtually nobody will explicitly
set `allowAliases = true;`.
