Implement deadline matching logic for dashboard repository and enhance unit tests

- Added the `deadlineWithinWindowMatch` function to match raw deadline fields stored as Unix seconds or milliseconds, ensuring accurate filtering in MongoDB queries.
- Updated the `ClosingSoon` method in the repository to utilize the new deadline matching logic, improving query accuracy for upcoming deadlines.
- Introduced a new unit test, `TestDeadlineWithinWindowMatchCoversSecondsAndMilliseconds`, to validate the functionality of the deadline matching logic, ensuring both seconds and milliseconds are correctly handled.
- Enhanced comments in the `widget_cache` and `search_list_cache` files for better clarity on cache behavior and staleness.

This update improves the accuracy of deadline handling in the dashboard service and strengthens the test coverage for related functionalities.

internal/dashboard/repository_test.go

@@ -42,3 +42,30 @@ func TestFacetCurrencyValueDecodesBSOND(t *testing.T) {
 		t.Fatalf("expected 12345.67, got %f", total)
 	}
 }
+
+func TestDeadlineWithinWindowMatchCoversSecondsAndMilliseconds(t *testing.T) {
+	now := int64(1_700_000_000)
+	windowEnd := now + 86_400
+
+	match := deadlineWithinWindowMatch("submission_deadline", now, windowEnd)
+	orClause, ok := match["$or"].(bson.A)
+	if !ok || len(orClause) != 2 {
+		t.Fatalf("expected two range branches, got %#v", match)
+	}
+
+	secRange, ok := orClause[0].(bson.M)["submission_deadline"].(bson.M)
+	if !ok {
+		t.Fatalf("expected seconds range on submission_deadline, got %#v", orClause[0])
+	}
+	if secRange["$gt"] != now || secRange["$lte"] != windowEnd {
+		t.Fatalf("unexpected seconds range: %#v", secRange)
+	}
+
+	msRange, ok := orClause[1].(bson.M)["submission_deadline"].(bson.M)
+	if !ok {
+		t.Fatalf("expected milliseconds range on submission_deadline, got %#v", orClause[1])
+	}
+	if msRange["$gt"] != now*1000 || msRange["$lte"] != windowEnd*1000 {
+		t.Fatalf("unexpected milliseconds range: %#v", msRange)
+	}
+}