test(member-live): build date-filter property bounds without a reject-filter

The bound-pair generator filtered out ~1/4 of generated values, so unlucky
seeds hit StreamData's FilterTooNarrowError under full property runs.
Construct an at-least-one-bound-set pair directly instead, preserving the
exact domain with no rejection.

test/mv_web/live/member_live/date_filter_property_test.exs

@@ -20,11 +20,12 @@ defmodule MvWeb.MemberLive.Index.DateFilterPropertyTest do
 
   # Generators -----------------------------------------------------------
 
+  defp date_gen do
+    map(integer(-3650..3650), &Date.add(~D[2000-01-01], &1))
+  end
+
   defp optional_date_gen do
-    one_of([
-      constant(nil),
-      map(integer(-3650..3650), &Date.add(~D[2000-01-01], &1))
-    ])
+    one_of([constant(nil), date_gen()])
   end
 
   defp exit_date_mode_gen do
@@ -57,19 +58,25 @@ defmodule MvWeb.MemberLive.Index.DateFilterPropertyTest do
 
   # Property -------------------------------------------------------------
 
+  # Generates a {from, to} pair with at least one bound set. Built by construction
+  # (pick which bounds are set, then generate the required dates) rather than by
+  # filtering out the both-nil case, so StreamData never rejects values and cannot
+  # raise FilterTooNarrowError on unlucky seeds.
   defp bound_pair_with_at_least_one_set_gen do
     gen all(
-          from <- optional_date_gen(),
-          to <- optional_date_gen(),
-          from != nil or to != nil
+          which <- member_of([:from_only, :to_only, :both]),
+          date_a <- date_gen(),
+          date_b <- date_gen()
         ) do
-      {from, to}
+      case which do
+        :from_only -> {date_a, nil}
+        :to_only -> {nil, date_a}
+        :both -> {date_a, date_b}
+      end
     end
   end
 
-  defp value_date_gen do
-    map(integer(-3650..3650), &Date.add(~D[2000-01-01], &1))
-  end
+  defp value_date_gen, do: date_gen()
 
   # Property -------------------------------------------------------------