modernize to 2.0: drop Python 2, refresh Unicode data through 17.0.0, fix collator selection

[jtauber]

A modernization pass bringing pyuca up to current Python packaging, tooling, and
Unicode data, released as 2.0.0.

Why

The default Collator was chosen from sys.version_info via a branch that
stopped at Python 3.6, so Python 3.7–3.14 all silently used UCA 9.0.0 (2016)
even though their unicodedata is 14.0–16.0. Because sort_key normalizes with
the standard library's unicodedata, the collator should track the runtime's
Unicode version — which is now what it does.

What changed

• Version selection driven by unicodedata.unidata_version instead of
  sys.version_info. On Python 3.14 the default is now Collator_16_0_0
  (was Collator_9_0_0).
• Unicode data refreshed — DUCET tables and Non-ignorable conformance
  suites added for 13.0.0, 14.0.0, 15.0.0, 15.1.0, 16.0.0 and 17.0.0. All
  tables are gzipped; scripts/fetch_ducet.py regenerates them.
• Generalized implicit weights — the hardcoded per-version CJK boolean
  flags are gone, replaced by fixed Han block boundaries plus the data file's
  own @implicitweights directives (handles Tangut/Nushu/Khitan and 17.0.0's
  reassigned bases).
• Dropped Python 2; now requires Python 3.11+. Full type hints,
  py.typed, and pyright (standard mode).
• Packaging moved to pyproject.toml + hatchling + uv; setup.py,
  setup.cfg, tox.ini, .travis.yml, MANIFEST.in removed.
• Tests migrated to pytest with a parametrized conformance suite; coverage
  is enforced at 100%.
• CI moved from Travis to GitHub Actions (Python 3.11–3.14, plus macOS and
  Windows spot checks).

Performance

• Parsed DUCET tables are cached per file: a second Collator() drops from
  ~52 ms to ~1.6 µs.
• collation_elements is now O(n) (index cursor instead of list.pop(0) and
  slicing); long-string sort keys are ~5× faster and no longer quadratic.

Validation

100% UCA conformance (Non-ignorable) on every version run on its matching
interpreter:

Python	Unicode	conformance
3.10	13.0.0	207268 / 0 fail
3.11	14.0.0	211448 / 0 fail
3.12	15.0.0	180108 / 0 fail
3.13	15.1.0	180158 / 0 fail
3.14	16.0.0	206315 / 0 fail

ruff, pyright, and pytest --cov (100%) all pass. The built wheel installs
clean and ships the gzipped tables and py.typed.

Breaking changes

• Requires Python 3.11+.
• The default collator now tracks the runtime's Unicode version, so sort keys
  for characters added since UCA 9.0.0 will differ from 1.x on modern Pythons.

Known limitations

• Only the Non-ignorable variable-weighting setting is implemented; the Shifted
  fixtures are bundled but not yet exercised.
• A version's conformance is only guaranteed on an interpreter whose
  unicodedata matches it. Collator_17_0_0 is included ahead of a CPython
  release shipping Unicode 17.