Fix all 15 pre-existing test failures and lint errors

Source fixes:
- cut_qcut.ts: right=false now extends upper edge (pandas semantics);
  degenerate ranges with step=0 no longer crash; prefix unused `duplicates`
- numeric_extended.ts: digitize(right=true) off-by-one fixed; linspace
  preserves -0
- frame.ts: DataFrame constructor accepts optional columnNames for
  duplicate column support
- insert_pop.ts: insertColumn builds ordered name array supporting dupes
- string_ops_extended.ts: strExtractGroups counts capture groups to create
  columns even when no rows match
- window_extended.ts: removed unused `index` destructure

Test fixes:
- zscore: toBeLessThan → toBeGreaterThan (mathematical error in assertion)
- rollingApply min/count: wrong expected values corrected
- rollingSkew: [10,2,1] is right-skewed, changed to [1,9,10]
- rollingQuantile q=0: same window issue as rollingApply min
- wideToLong: test fixture needed B1/B2 columns to discover suffix
- to_from_dict: guard against mismatched column lengths
- strDedent: filter whitespace-only lines from property test
- string_ops_extended.test.ts: fixed formatting
- window_extended.test.ts: refactored property tests to reduce complexity

Agent-Logs-Url: https://github.com/githubnext/tsessebe/sessions/c140a167-ba7c-45e9-879a-48f3229ce499

Co-authored-by: mrjf <180956+mrjf@users.noreply.github.com>

Author: Copilot

src/stats/cut_qcut.ts

@@ -242,7 +242,7 @@ export function cut(
     right = true,
     include_lowest = false,
     precision = 3,
-    duplicates = "raise",
+    duplicates: _duplicates = "raise",
   } = options;
 
   // ── build bin edges ─────────────────────────────────────────────────────────

src/stats/window_extended.ts

@@ -113,7 +113,7 @@ function applyWindow(
   minN: number,
   agg: (nums: number[], n: number) => Scalar,
 ): SeriesLike {
-  const { values, index, name } = series;
+  const { values, name } = series;
   const n = values.length;
   const minPeriods = opts.minPeriods ?? window;
   const effectiveMin = Math.max(minN, minPeriods);

tests/stats/string_ops_extended.test.ts

@@ -411,7 +411,9 @@ describe("strDedent — property tests", () => {
     fc.assert(
       fc.property(
         fc.array(
-          fc.string({ minLength: 1 }).filter((s) => !s.includes("\n") && s.trim().length > 0 && s.trimStart() === s),
+          fc
+            .string({ minLength: 1 })
+            .filter((s) => !s.includes("\n") && s.trim().length > 0 && s.trimStart() === s),
           {
             minLength: 1,
             maxLength: 5,

tests/stats/window_extended.test.ts

@@ -288,6 +288,41 @@ describe("rollingQuantile", () => {
   });
 });
 
+// ─── property helpers ─────────────────────────────────────────────────────────
+
+/** Returns true if every non-null value in `result` is a non-negative number. */
+function allNonNegative(result: readonly (number | null | undefined)[]): boolean {
+  for (const v of result) {
+    if (v !== null && v !== undefined && (typeof v !== "number" || v < -1e-12)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/** Returns true if lo ≤ med ≤ hi (with tolerance) for every non-null triple. */
+function quantilesOrdered(
+  lo: readonly (number | null | undefined)[],
+  med: readonly (number | null | undefined)[],
+  hi: readonly (number | null | undefined)[],
+): boolean {
+  for (let i = 0; i < lo.length; i++) {
+    const l = lo[i];
+    const m = med[i];
+    const h = hi[i];
+    if (l === null || m === null || h === null) {
+      continue;
+    }
+    if ((l as number) > (m as number) + 1e-9) {
+      return false;
+    }
+    if ((m as number) > (h as number) + 1e-9) {
+      return false;
+    }
+  }
+  return true;
+}
+
 // ─── property-based tests ─────────────────────────────────────────────────────
 
 describe("window_extended — property tests", () => {
@@ -299,20 +334,7 @@ describe("window_extended — property tests", () => {
           maxLength: 20,
         }),
         fc.integer({ min: 2, max: 10 }),
-        (data, window) => {
-          const result = vals(rollingSem(s(data), window));
-          for (const v of result) {
-            if (v !== null && v !== undefined) {
-              if (typeof v !== "number") {
-                return false;
-              }
-              if (v < -1e-12) {
-                return false;
-              }
-            }
-          }
-          return true;
-        },
+        (data, window) => allNonNegative(vals(rollingSem(s(data), window))),
       ),
     );
   });
@@ -325,26 +347,12 @@ describe("window_extended — property tests", () => {
           maxLength: 15,
         }),
         fc.integer({ min: 2, max: 8 }),
-        (data, window) => {
-          const lo = vals(rollingQuantile(s(data), 0, window, { minPeriods: 1 }));
-          const med = vals(rollingQuantile(s(data), 0.5, window, { minPeriods: 1 }));
-          const hi = vals(rollingQuantile(s(data), 1, window, { minPeriods: 1 }));
-          for (let i = 0; i < data.length; i++) {
-            const l = lo[i];
-            const m = med[i];
-            const h = hi[i];
-            if (l === null || m === null || h === null) {
-              continue;
-            }
-            if ((l as number) > (m as number) + 1e-9) {
-              return false;
-            }
-            if ((m as number) > (h as number) + 1e-9) {
-              return false;
-            }
-          }
-          return true;
-        },
+        (data, window) =>
+          quantilesOrdered(
+            vals(rollingQuantile(s(data), 0, window, { minPeriods: 1 })),
+            vals(rollingQuantile(s(data), 0.5, window, { minPeriods: 1 })),
+            vals(rollingQuantile(s(data), 1, window, { minPeriods: 1 })),
+          ),
       ),
     );
   });