Iteration 147: strSplitExpand, strExtractGroups, strPartition, strRPartition, strMultiReplace, strIndent, strDedent

Added src/stats/string_ops_extended.ts — 7 standalone advanced string operations:
- strSplitExpand: split strings and expand parts to DataFrame columns (mirrors pandas str.split(expand=True))
- strExtractGroups: extract regex capture groups (named or numbered) to DataFrame (mirrors pandas str.extract)
- strPartition / strRPartition: split at first/last occurrence of sep → (before, sep, after) tuple or DataFrame
- strMultiReplace: apply multiple find/replace pairs in sequence (string literals or RegExp)
- strIndent: prefix every non-empty line with a string (mirrors textwrap.indent)
- strDedent: remove common leading whitespace from all lines (mirrors textwrap.dedent)

All functions use TypeScript overloads for scalar vs Series/array dispatch. 50+ unit tests + 4 property-based tests (fast-check). Playground page string_ops_extended.html with interactive demos for all 7 functions.

Run: https://github.com/githubnext/tsessebe/actions/runs/24206383170

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

playground/index.html

@@ -304,6 +304,11 @@ <h3><a href="string_ops.html" style="color: var(--accent); text-decoration: none
           <p>Module-level string utilities: <code>strNormalize</code> (Unicode NFC/NFD/NFKC/NFKD), <code>strGetDummies</code> (one-hot DataFrame), <code>strExtractAll</code> (all regex matches), <code>strRemovePrefix</code>, <code>strRemoveSuffix</code>, <code>strTranslate</code> (char-level substitution), <code>strCharWidth</code> (CJK-aware display width), <code>strByteLength</code>. Works on Series, arrays, or scalars.</p>
           <div class="status done">✅ Complete</div>
         </div>
+        <div class="feature-card">
+          <h3><a href="string_ops_extended.html" style="color: var(--accent); text-decoration: none;">🔤 string_ops_extended — Extended String Ops</a></h3>
+          <p>Advanced string utilities: <code>strSplitExpand</code> (split → DataFrame columns), <code>strExtractGroups</code> (regex capture groups → DataFrame), <code>strPartition</code> / <code>strRPartition</code> (split into before/sep/after), <code>strMultiReplace</code> (batch replacements), <code>strIndent</code> / <code>strDedent</code> (line-level indentation). Works on Series, arrays, or scalars.</p>
+          <div class="status done">✅ Complete</div>
+        </div>
         <div class="feature-card">
           <h3><a href="pipe_apply.html" style="color: var(--accent); text-decoration: none;">🔗 pipe_apply — Pipeline &amp; Apply Utilities</a></h3>
           <p>Standalone equivalents of pandas' <code>pipe()</code> / <code>apply()</code> / <code>applymap()</code>: <code>pipe</code> (variadic type-safe pipeline), <code>seriesApply</code> (element-wise with label/pos context), <code>seriesTransform</code>, <code>dataFrameApply</code> (axis 0/1), <code>dataFrameApplyMap</code> (cell-wise), <code>dataFrameTransform</code> (column-wise), <code>dataFrameTransformRows</code> (row-wise).</p>