fix(deps): pin typing-extensions to one version so uv.lock parses in CI

Adding the myst-nb docs stack pulled a newer typing-extensions only on
Python < 3.11, splitting it into two locked versions. Our own
`typing-extensions; python_full_version < '3.13'` dependency then spanned
that split, which uv recorded as a multi-version edge without a `version`
field — a form older uv builds (the one in CI's pinned setup-uv) reject
with "missing source field but has more than one matching package".

Add a [tool.uv] constraint-dependencies pin of typing-extensions>=4.15.0
so it resolves to a single version across all supported Pythons, removing
the fork and the under-specified edge. Relocked; uv lock --locked is clean
and no multi-version package has a marker-only edge.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: timsaucer

pyproject.toml

@@ -192,6 +192,16 @@ skip = [
 count = true
 ignore-words-list = ["IST", "ans"]
 
+[tool.uv]
+# Keep typing-extensions on a single version across all supported Pythons.
+# Adding the docs `myst-nb` stack pulled a newer typing-extensions only on
+# Python < 3.11, splitting it into two locked versions. Our own
+# `typing-extensions; python_full_version < '3.13'` dependency then spanned
+# that split, which uv records as an under-specified lock entry that older
+# uv versions (such as the one in CI) refuse to parse. Pinning to one
+# version removes the fork.
+constraint-dependencies = ["typing-extensions>=4.15.0"]
+
 [dependency-groups]
 dev = [
   "arro3-core==0.6.5",