docs: suppress intersphinx inventory warnings in CI

Add intersphinx_timeout and suppress intersphinx.external warnings so
that unreachable inventories (e.g. pandas 522 errors) don't fail the
--fail-on-warning build.

Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: joseph-isaacs

docs/conf.py

@@ -52,6 +52,11 @@
     "numpy": ("https://numpy.org/doc/stable", None),
     "polars": ("https://docs.pola.rs/api/python/stable", "polars.objects.inv"),
 }
+intersphinx_timeout = 10
+
+suppress_warnings = [
+    "intersphinx.external",
+]
 
 git_root = Path(__file__).parent.parent