Previously f150387 fixed the priority of
ansible_become_pass over ansible_become_password, but broke --ask-become-pass.
Fixes mitogen-hq#952.

Should have higher uptime, and make us less of a burden. Refs mitogen-hq#1058

Fix --ask-become-pass

This
- Clarifies and corrects docstrings and comments based on investigation for mitogen-hq#957
- Removes unused `Poller*._repr` attributes
- Eliminates some uses of `getattr()`
- Introduces `mitogen.parent.POLLERS` & `mitogen.parent.POLLER_LIGHTWEIGHT`

Preamble size change
```
@@ -1,7 +1,7 @@
 SSH command size: 759
-Bootstrap (mitogen.core) size: 17862 (17.44KiB)
+Bootstrap (mitogen.core) size: 17934 (17.51KiB)

                               Original          Minimized           Compressed
-mitogen.parent            98171 95.9KiB  50569 49.4KiB 51.5%  12742 12.4KiB 13.0%
+mitogen.parent            96979 94.7KiB  49844 48.7KiB 51.4%  12697 12.4KiB 13.1%
 mitogen.fork               8436  8.2KiB   4130  4.0KiB 49.0%   1648  1.6KiB 19.5%
 mitogen.ssh               10892 10.6KiB   6952  6.8KiB 63.8%   2113  2.1KiB 19.4%
```

…kerProcess

`mitogen.parent.POLLER_LIGHTWEIGHT` will normally be `PollPoller`, falling
back to `EpollPoller`, `KqueuePoller`, or `Poller`.

Fixes mitogen-hq#957

Co-authored-by: Luca Berruti <[email protected]>
Co-authored-by: Philippe Kueck <[email protected]>

ansible_mitogen: Fix "filedescriptor out of range in select()" in WorkerProcess

adding new hosts to the inventory using 'add_hosts'

Co-authored-by: Alex Willmer <[email protected]>

refs mitogen-hq#1066

Some tests were being incorrectly excluded. Including those that use
`add_host`.
refs mitogen-hq#1066, mitogen-hq#1069

Fix add_hosts when ansible_host_key_checking is passed to the new host

integration/ssh/timeouts.yml is noteworthy. It was an accidental N**2 in time
-  executing num hosts * num hosts tasks.

Speed up test suite

CentOS 8 has reached EOL. Packages are no longer mirrored or maintained. A
historic snapshot of the packages is kept on vault.centos.org.

refs mitogen-hq#1088, mitogen-hq#1090

macOS 11 is not longer an available runner on Azure Devops. The minimum is now
macOS 12. This runner does not have Python 2.7 installed, so running them
would require a custom install - which I'm declaring too much effort for too
little gain.

refs mitogen-hq#1090

Pip 72 was released yesterday (2024-07-28), dropping `setup.py test` support.
hdrhistogram 0.6.1 requires it to install.

For now constrain Pip to earlier releases, so our tests can be run.

refs mitogen-hq#1090

ci: Summer 2024 test fixups

…v0.3.8