feat(oscillators): add DSO - Ehlers Deviation-Scaled Oscillator

Implement DSO (TASC Oct 2018) with SSF 2-pole filter, RMS normalization,
and Fisher Transform (±0.99 clamp). Sealed class, O(1) streaming RMS via
RingBuffer, precomputed SSF coefficients.

New files: Dso.cs, Dso.Quantower.cs, Dso.md, dso.pine,
  Dso.Tests.cs (27), Dso.Validation.Tests.cs (7), Dso.Quantower.Tests.cs (11)

Updated: Exports.cs, _bridge.py, oscillators.py, SPEC.md,
  _sidebar.md, lib/_index.md, oscillators/_index.md,
  docs/indicators.md, docs/pinescript.md

All 19,565 tests pass, 0 warnings.

python/quantalib/_bridge.py

@@ -447,6 +447,7 @@ HAS_KRI = _bind("qtl_kri", [_dp, _ci, _dp, _ci])
 HAS_PSL = _bind("qtl_psl", [_dp, _ci, _dp, _ci])
 HAS_DECO = _bind("qtl_deco", [_dp, _ci, _dp, _ci, _ci])
 HAS_DOSC = _bind("qtl_dosc", [_dp, _ci, _dp, _ci, _ci, _ci, _ci])
+HAS_DSO = _bind("qtl_dso", [_dp, _ci, _dp, _ci])
 HAS_DYMI = _bind("qtl_dymi", [_dp, _ci, _dp, _ci, _ci, _ci, _ci, _ci])
 HAS_CRSI = _bind("qtl_crsi", [_dp, _ci, _dp, _ci, _ci, _ci])
 HAS_BBB = _bind("qtl_bbb", [_dp, _ci, _dp, _ci, _cd])

python/quantalib/oscillators.py

@@ -49,6 +49,7 @@ __all__ = [
     "psl",
     "deco",
     "dosc",
+    "dso",
     "dymi",
     "crsi",
     "bbb",
@@ -547,6 +548,14 @@ def dosc(close: object, rsi_period: int = 14, ema1_period: int = 5,
     return _wrap(dst, idx, f"DOSC_{rsi_period}", "oscillators", offset)
 
 
+def dso(close: object, period: int = 40, offset: int = 0, **kwargs) -> object:
+    """Ehlers Deviation-Scaled Oscillator."""
+    period = int(kwargs.get("length", period)); offset = int(offset)
+    src, idx = _arr(close); n = len(src); dst = _out(n)
+    _check(_lib.qtl_dso(_ptr(src), n, _ptr(dst), period))
+    return _wrap(dst, idx, f"DSO_{period}", "oscillators", offset)
+
+
 def dymi(close: object, base_period: int = 14, short_period: int = 5,
          long_period: int = 10, min_period: int = 3, max_period: int = 30,
          offset: int = 0, **kwargs) -> object: