Add a 7-day cooldown to Dependabot checks

So that Dependabot won't open PRs for updates that are less than 7 days old, to reduce the risk of getting caught up in supply chain attacks. The use of cargo-vet already prevents CI builds from passing with un-vetted dependency versions, but this should save a little effort for Python and Node.js dependencies.

Cooldowns aren't supported for GitHub Actions dependencies.

.github/dependabot.yml

@@ -4,6 +4,8 @@ updates:
   directory: "/"
   schedule:
     interval: weekly
+  cooldown:
+    default-days: 7
 
 - package-ecosystem: uv
   directories:
@@ -11,11 +13,15 @@ updates:
     - /python
   schedule:
     interval: weekly
+  cooldown:
+    default-days: 7
 
 - package-ecosystem: npm
   directory: /nodejs
   schedule:
     interval: weekly
+  cooldown:
+    default-days: 7
 
 - package-ecosystem: github-actions
   directory: "/"