fix(cd): include LICENSE in sdist + skip-existing PyPI uploads

CD #64 (run 25943880454) successfully uploaded all 4 wheels (linux
x86_64/aarch64, macos arm64, windows x86_64) to PyPI as treemapper
1.6.1 but then 400'd on the sdist with 'License-File LICENSE does not
exist in distribution file'. Cause: maturin only ships files matching
[tool.maturin].include in the sdist tarball, and LICENSE was not in
that list. The wheel auto-embeds LICENSE via PEP 639 metadata so it
passed; the sdist did not.

- pyproject.toml: add LICENSE, README.md, CHANGELOG.md to the maturin
  sdist include list. Verified locally: 'maturin sdist' now produces
  a tarball that contains treemapper-1.6.1/LICENSE.
- cd.yml: set skip-existing: true on pypa/gh-action-pypi-publish so
  re-running CD for v1.6.1 silently skips the already-published wheels
  and only uploads the new (fixed) sdist.

Author: nikolay-e

.github/workflows/cd.yml

@@ -313,6 +313,11 @@ jobs:
         with:
           packages-dir: ./dist
           print-hash: true
+          # Idempotent re-runs: if a wheel for this version was already
+          # uploaded in a previous (failed) CD run, skip it instead of
+          # erroring out. New artifacts (e.g. a corrected sdist) still
+          # publish.
+          skip-existing: true
 
   smoke-pypi:
     name: Post-publish smoke test (${{ matrix.os }} / py${{ matrix.python-version }})

pyproject.toml

@@ -117,6 +117,9 @@ module-name = "treemapper._diffctx"
 manifest-path = "diffctx/Cargo.toml"
 features = [ "pyo3/extension-module", "python" ]
 include = [
+  { path = "LICENSE", format = "sdist" },
+  { path = "README.md", format = "sdist" },
+  { path = "CHANGELOG.md", format = "sdist" },
   { path = "diffctx/Cargo.toml", format = "sdist" },
   { path = "diffctx/Cargo.lock", format = "sdist" },
   { path = "diffctx/src/**/*", format = "sdist" },