test(traffic): keep the timing test's Vite cache out of the package tree

The traffic timing test starts a Vite server rooted at the package, which
wrote its dependency cache to node_modules/.vite and kept writing after the
server closed. A host running Core's suite then finds files inside Core and
its check refuses them. The server now uses a temporary cache directory,
removed afterwards, and skips dependency discovery, which the SSR-loaded
modules never need.

The HUD place-lookup changelog note credits its PR, #1459.

changelog.d/1459-hud-place-lookups.md

@@ -2,4 +2,4 @@
   looks up place names when no OpenAI key is configured, reverse-geocodes at
   most two points instead of up to four, and looks up again only once the view
   shows a different area, not after every small pan, so a small pan no longer
-  asks OpenAI for a new summary either (samehkhamis, #0000).
+  asks OpenAI for a new summary either (samehkhamis, #1459).