Upgrade dev dependencies

Update dev dependencies to latest compatible versions:
- ruff: 0.12.0 -> 0.14.2
- coverage: 7.9.1 -> 7.10.6 (latest supporting Python 3.9)

Note: coverage 7.11.0+ requires Python 3.10+, so we stay at 7.10.x
to maintain Python 3.9 support. These are dev-only changes and don't
affect library users.

Author: vertti

pyproject.toml

@@ -40,9 +40,9 @@ dev = [
     "pyrefly",
     "pytest-mock>=3.14.1",
     "pytest-cov>=6.0.0",
-    "coverage[toml]>=7.9.1",
+    "coverage[toml]>=7.10.6",
     "pydocstyle>=6.3.0",
-    "ruff>=0.12.0",
+    "ruff>=0.14.2",
     "pandas>=1.5.1,<3.0.0",
     "polars>=1.7.0",
 ]