Various fixes to lazy imports

[jdemeyer]

Assorted fixes to lazy imports:

1. Drop support for lazy_import(overwrite=False) which was used only in one place in a dubious way to implement a 2-level lazy import (a lazy import being lazily imported).

2. More optimal code for binary operations like __add__ by avoiding the operator module.

3. Move the code to replace a lazy import in a class namespace from _get_object() to __get__.

4. Partially inline _get_object() with a new cdef inline function for the case that the object has been initialized.

5. A lazy import without at_startup being imported at startup is now an error (it used to just print a message, which is less useful than an error traceback).

6. Implement matmul (pointless in Python 2, but useful for Python 3).

7. Clean up the function lazy_import a bit.

Component: misc

Author: Jeroen Demeyer

Branch/Commit: 4dda1ae

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/22755

[jdemeyer]

Branch: u/jdemeyer/ticket/22755

[jdemeyer]

Commit: d2bb491

[jdemeyer]

New commits:

94302ca	Do not declare functions/methods as "cdef inline"
9e5715e	Various improvements to lazy imports
d2bb491	Whitespace fix

[jdemeyer]

Description changed:

--- 
+++ 
@@ -1 +1,13 @@
-Assorted fixes to lazy imports.
+Assorted fixes to lazy imports:
+
+1. Drop support for `lazy_import(overwrite=False)` which was used only in one place in a dubious way to implement a 2-level lazy import (a lazy import being lazily imported).
+
+2. More optimal code for binary operations like `__add__` by avoiding the `operator` module.
+
+3. Move the code to replace a lazy import in a class namespace from `_get_object()` to `__get__`.
+
+4. A lazy import without `at_startup` being imported at startup is now an error (it used to just print a message, which is less useful than an error traceback).
+
+5. Implement `__matmul__` (pointless in Python 2, but useful for Python 3).
+
+6. Clean up the function `lazy_import` a bit.

[jdemeyer]

Description changed:

--- 
+++ 
@@ -8,6 +8,6 @@
 
 4. A lazy import without `at_startup` being imported at startup is now an error (it used to just print a message, which is less useful than an error traceback).
 
-5. Implement `__matmul__` (pointless in Python 2, but useful for Python 3).
+5. Implement [__matmul__](https://www.python.org/dev/peps/pep-0465/) (pointless in Python 2, but useful for Python 3).
 
 6. Clean up the function `lazy_import` a bit.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

8aac18a

Various improvements to lazy imports

[sagetrac-git]

Changed commit from d2bb491 to 8aac18a

[sagetrac-git]

Changed commit from 8aac18a to f3ede00

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

f3ede00

Use exact type check in obj()

[jdemeyer]

Changed dependencies from #22753 to none

[sagetrac-git]

Changed commit from f3ede00 to 7bf2ce8