Assert filterDateRange input is sorted ascending (#38)

The binary-search filterDateRange overload assumes its collection is sorted
ascending by startDate, but returns silently-wrong results otherwise. Add a
debug-only assert enforcing that contract (compiled out of release builds, so
no runtime cost).

This immediately surfaced an existing violation: testGlucoseEffectFromHistory
built a `basal` schedule with segments out of order (and one with endDate
before startDate, plus overlaps). Replace it with a well-formed sorted,
contiguous, non-overlapping schedule, and regenerate the expected-effect
fixture to match the corrected schedule.

Author: ps2

Sources/LoopAlgorithm/SampleValue.swift

@@ -111,6 +111,13 @@ public extension Sequence where Element: TimelineValue {
 public extension RandomAccessCollection where Element: TimelineValue, Index == Int {
     func filterDateRange(_ startDate: Date?, _ endDate: Date?) -> [Element] {
         guard !isEmpty else { return [] }
+        // This binary-search filter is only correct when the elements are sorted
+        // ascending by startDate. Catch contract violations in debug builds; the
+        // check is compiled out of release builds, so there is no runtime cost.
+        assert(
+            zip(self, dropFirst()).allSatisfy { $0.startDate <= $1.startDate },
+            "filterDateRange requires elements sorted ascending by startDate"
+        )
         // Lower bound: first index where element.endDate >= startDate
         var lo = startIndex
         if let startDate {