feat(routes)!: require dependencies in add_routes and hide previews by default

[allen0099]

Closes #298. The 0.3.9 warning was #301.

Changes

• add_routes(app, prefix="", include_in_schema=False, *, dependencies, include_content_preview=False):
  • dependencies is required and keyword-only. Pass a guard, or dependencies=[] to mount the routes unguarded on purpose.
  • Passing None raises TypeError, with a message that names both fixes. Leaving dependencies out gets Python's own "missing required keyword-only argument" error. Type checkers flag both.
  • include_content_preview defaults to False. It also becomes keyword-only, because it follows dependencies.
  • prefix and include_in_schema can still be passed by position.
• The 0.3.9 UserWarning is removed.
• Docs, in docs/ and i18n/zh-TW/docs/:
  • HTTP_CACHING: the example shows include_content_preview=True, and the warning box states that dependencies is required.
  • MIGRATING_0_4:
    • explains the keyword-only arguments and the TypeError;
    • lists the two cases 0.3.9 did not warn about: positional calls, and relying on the preview default while passing dependencies;
    • the summary table states that 0.3.9 warned only when dependencies was left out.
• Changelog fragment changelog.d/298.changed.md.

Tests

• TestDependenciesRequired covers:
  • leaving dependencies out;
  • None, which raises and mounts no route;
  • a 0.3.x positional call;
  • [], which mounts the routes unguarded;
  • prefix and include_in_schema passed by position.
• The preview test is parametrized over the default and False.
• Mutation check: each of these makes exactly one test fail:
  • removing the None check;
  • flipping the preview default back to True;
  • giving dependencies a default.
• Full suite, including the live Redis/Memcached tests: 1586 passed, 1 skipped, coverage 99.82%.
• mypy (strict package, tests, scripts), pre-commit, both strict docs builds and tox -e lowest pass.