chore: adopt the NAPALM driver standard

- CI moves to .gitea/workflows/ci.yml and calls the shared driver workflow
  of NAPALM/driver-standard; .github/ is gone.
- requires-python >=3.10 (napalm-device-types needs it), floor
  napalm-device-types>=4.21.1 (was napalm_device_types>=0.4.0), LICENSE
  file, py.typed, SPDX license string, links to git.netork.io, a dev extra
  with floors.
- README (pyproject named one that did not exist) and CHANGELOG.md.
- mypy strict for the package; napalm_zyxel.zyxel_driver is exempt for now
  (24 errors), recorded in the quality baseline with its two complex
  functions. Coverage floor 68 % (measured 68.97 %).

Closes #8

CHANGELOG.md

@@ -0,0 +1,16 @@
+# Changelog
+
+All notable changes to this driver. The format follows
+[Keep a Changelog](https://keepachangelog.com/), versions follow
+[Semantic Versioning](https://semver.org/).
+
+## [Unreleased]
+
+### Changed
+- The driver follows the NAPALM driver standard
+  (https://git.netork.io/NAPALM/driver-standard): CI on Gitea runs ruff, mypy, the
+  tests on Python 3.10–3.13 and at the lowest declared versions, bandit, pip-audit and
+  a build check, and a release tag publishes to PyPI. The package now ships `py.typed`,
+  a README and a LICENSE file. **Python 3.9 is no longer supported**; napalm-device-types
+  never ran on it. It needs napalm-device-types 4.21.1 or later.
+- A failed login keeps the underlying error as the cause of the `ConnectionException`.