fix(ci): retry PyPI install in verify step to handle indexing delay

PyPI can take 30-90s to index a newly uploaded wheel. The smoke test was
running immediately after publish completed and hitting the window before
indexing finished. Added a retry loop (5 attempts, 30s backoff) matching
the same pattern already used for crates.io.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: akollegger

.github/workflows/publish.yml

@@ -239,5 +239,9 @@ jobs:
         env:
           RELEASE_VERSION: ${{ needs.validate.outputs.version }}
         run: |
-          python -m pip install "relateby-pattern==${RELEASE_VERSION}"
+          for i in 1 2 3 4 5; do
+            python -m pip install "relateby-pattern==${RELEASE_VERSION}" && break
+            echo "Attempt $i/5: PyPI not yet indexed, retrying in 30s..."
+            sleep 30
+          done
           python scripts/release/python-smoke.py --expect-distribution relateby-pattern