fix(shipwrecks): the page clears shown wrecks as a whole, once even the newest source is too old

Removing one source's wrecks on the page split merged records: a wreck both
sources list is one Wikidata record carrying EMODnet facts, so expiring
Wikidata dropped wrecks EMODnet still had, and expiring EMODnet kept its
facts. The page now keeps every shown wreck, marked stale, until the newest
source passes the limit, then clears them all. Adds a source test for the
reported ages and limit.

scripts/format-scope.json

@@ -1280,6 +1280,7 @@
   "src/layers/shipwrecks/eras.test.mjs",
   "src/layers/shipwrecks/period.test.mjs",
   "src/layers/shipwrecks/index.test.mjs",
+  "src/layers/shipwrecks/source.test.mjs",
   "src/data/shipwrecksProxy.test.mjs",
   "src/app/sourceComposition.js",
   "src/app/sourceComposition.test.mjs",