chore: make Python 3.11 the consistently declared minimum

[mdwcrft]

Problem

Since 2.1.0, pyproject.toml has required python = "^3.11", but the rest of the repo disagrees:

• The classifiers still list 3.8, 3.9 and 3.10.
• docs/source/installation.rst says "Python 3.7 or higher".

This mismatch is what #740 reported: on 3.10 (for example Ubuntu 22.04), pip silently skips 2.1.0 even though the metadata and docs say 3.10 is supported.

Decision: keep the 3.11 minimum rather than lowering it

#740 proposed lowering the minimum to 3.9. We're not doing that:

• 3.9 reached end-of-life in October 2025, and 3.10 reaches it in October 2026.
• Lowering the minimum would mean dependency markers and keeping old tooling working (sphinx 8 needs ≥3.11, black 26 needs ≥3.10) for interpreters that no longer get security fixes.
• Users on older Pythons can still install older ocpp releases, because pip only picks releases whose requires-python matches the running interpreter.

Policy, now written in the docs: support every CPython version that has not reached end-of-life. Add new versions when they're released, and drop a version in the first minor release after it reaches end-of-life.

Changes

• pyproject.toml:

  • Classifiers are now 3.11–3.14 plus Python :: 3 :: Only.
  • Removed a stale comment about Python 3.8 and asynctest.

• docs/source/installation.rst: changed to "Python 3.11 or higher" and added a "Supported Python versions" section with the policy above.

• .github/workflows/pull-request.yml: added 3.14 to the test matrix (the matrix checks the interpreter since ci: run the test matrix on the actual matrix interpreter, split lint from tests #768). The lint job now runs on 3.14.

• .github/workflows/publish-to-pypi.yml: publishes using 3.14.

• poetry.lock: bumped rpds-py 0.20.1 → 2026.6.3 (a transitive dependency via jsonschema/referencing) and markupsafe 3.0.2 → 3.0.4. Neither old version has 3.14 wheels, and building rpds-py from source fails on 3.14 because its bundled PyO3 only supports up to 3.13. No direct dependencies changed.

Verification

• make tests (lint + 184 tests) passes locally in fresh Poetry venvs bound to 3.11 and 3.14, with the interpreter and the rpds-py version confirmed inside each venv.
• On 3.14, pytest-asyncio 0.26 emits asyncio.*_event_loop_policy deprecation warnings. They come from the test dependency, not from ocpp, and can be handled in a separate dev-dependency bump.
• The built wheel's metadata has Requires-Python: >=3.11,<4.0 and classifiers for 3.11–3.14 only.

Supersedes #740.

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