build: replace hatchling with the uv_build backend and bump uv to 0.12

[vdusek]

Switches the build backend from hatchling to uv_build, replacing the [tool.hatch.build.targets.*] config with [tool.uv.build-backend]. Only CHANGELOG.md and CONTRIBUTING.md need an explicit source-include - the module, pyproject.toml, README, and LICENSE are in the sdist by default. The [tool.hatch.metadata] allow-direct-references setting is dropped, no dependency uses a direct reference.

License metadata moves to PEP 639: license = "Apache-2.0" plus license-files = ["LICENSE"]. That part is required, not cosmetic: uv_build ships LICENSE inside the wheel only when it is declared via license-files, and uv rejects license-files combined with the legacy license = { file = ... } table.

The License :: OSI Approved :: Apache Software License classifier is dropped because PEP 639 deprecates license classifiers in favor of License-Expression, which now carries the same information ("Using license classifier in the Classifier Core Metadata field is deprecated and replaced by the more precise License-Expression field"). See also the core metadata spec. uv warns about the classifier on every build.

The uv guide's Dockerfile now pulls ghcr.io/astral-sh/uv:0.12 (in docs/ and in the version-4.0 docs snapshot; the version-3.4 snapshot is left on 0.11).

Verified by building sdist + wheel before and after: the wheel contents are identical, and the metadata differs only in License-Expression: Apache-2.0 replacing the inlined license text. The sdist drops .gitignore and gains pyproject.toml.orig (uv 0.12 writes a TOML 1.0-compatible pyproject.toml into the sdist and keeps the original alongside it). uv.lock is unchanged.

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (67445ba) to head (0b5afe9).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1067      +/-   ##
==========================================
+ Coverage   91.83%   91.89%   +0.06%     
==========================================
  Files          51       51              
  Lines        3232     3232              
==========================================
+ Hits         2968     2970       +2     
+ Misses        264      262       -2     

Flag	Coverage Δ
e2e	35.33% <ø> (ø)
integration	57.08% <ø> (ø)
unit	83.26% <ø> (+0.06%)	⬆️

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