eager_import

[mkoeppe]

This would be just like lazy_import but actually eager (= equivalent to an ordinary import statement). Hence it would be suitable everywhere, including for importing classes that will be subclassed (see #33384).

On import failures, it would however not raise an error but provide a binding to a LazyImport instance that reports the failure on first use (and can give package installation advice -> discoverability).

We would use this mechanism in sage.all.

CC: @tobiasdiez @kwankyu

Component: refactoring

Issue created by migration from https://trac.sagemath.org/ticket/33820