Improve API documentation about typing

This also removes the redundant type annotations from the API example.
I think they make it harder to understand.

dev gitignore: add .nox

internal formatters: move another import under if TYPE_CHECKING:

backends libdnf5: restore the old get_releasever implementation

This partially reverts commit 467bdfe865d30d98676e9c7d3a1f7324f0ca3b6e.
See explanation in the code comments for why this was reverted.

Ref: https://github.com/rpm-software-management/dnf5/issues/281
Ref: https://github.com/rpm-software-management/dnf5/pull/1804

doc dnf-repoquery-diff: clarify Default repositories section

doc NEWS: properly give credit to contributors

Post release version bump

Release 1.4.0

data: add koji{,-src} aliases to epel and epel-next releases

ci: update locked dependencies

packaging: fix pytest invocation

Setting pythonpath in the pytest config is not supported by EL 9's
pytest version, so let's call python3 -m pytest which already includes
the current directory.

tests integration: skip network tests when running in mock

ci main: add python3-libdnf5 dependency

doc API: add note about experimental code

lint doc API: use semantic line breaks

doc API: remove outdated note about beta status

experimental: add warning about stability to exp. code

data: clean up CentOS Stream release configs

This makes the definitions DRY-er by using the "@[group]" syntax instead
of repeating repo IDs. Also, there's no need to disable system_repos
here. The repositories already have unique names to avoid conflicts.

data: adjust releases.toml for new EPEL 10+ branching model

`epelX` now track CentOS Stream for X >= 10, so there is no more
`epelX-next` with X >= 10:

https://discussion.fedoraproject.org/t/epel-10-status-update/124549/2

This causes noise when using the `fedrq` Python API, and the CLI just
flat out fail when querying with `-b c10s -r @epel` when it could not
refresh `epel10-next`.

Adjust the mapping: previous `centos-stream` copied over to
`centos-stream9` matching c9s only, and `centos-stream` modified to
match 10+ and drop `epel-next*`.

Tested:

```
$ fedrq pkgs retsnoop -b c10s -r @epel
retsnoop-0.10.1-2.el10_0.src
retsnoop-0.10.1-2.el10_0.x86_64

$ fedrq pkgs retsnoop -b c9s

$ fedrq pkgs retsnoop -b c9s -r @epel
retsnoop-0.10.1-1.el9.src
retsnoop-0.10.1-1.el9.x86_64

$ fedrq pkgs rmol -b c9s

$ fedrq pkgs rmol -b c9s -r @epel
rmol-1.00.11-1.el9.next.src
rmol-1.00.11-1.el9.next.x86_64

$ fedrq pkgs rmol -b ubi9

$ fedrq pkgs rmol -b ubi9 -r @epel
rmol-1.00.8-1.el9.src
rmol-1.00.8-1.el9.x86_64
```

Signed-off-by: Michel Lind <salimma@fedoraproject.org>

backends: add experimental support for comps