feat(apo): add Absolute Price Oscillator

EMA(close, fast) - EMA(close, slow). Like MACD without the signal EMA.
Defaults to (fast = 12, slow = 26); fast must be strictly less than
slow.

Touchpoints: apo.rs + mod.rs + lib.rs re-export, PyApo + __init__.py
+ test_new_indicators SCALAR + test_known_values flat reference,
ApoNode + index.d.ts/index.js + indicators.test.js factory + reference,
WasmApo via scalar macro, scalar-fuzz target, README + CHANGELOG.

bindings/python/python/wickra/__init__.py

@@ -56,6 +56,7 @@ from ._wickra import (
     PMO,
     StochRSI,
     UltimateOscillator,
+    APO,
     PPO,
     DPO,
     Coppock,
@@ -137,6 +138,7 @@ __all__ = [
     "PMO",
     "StochRSI",
     "UltimateOscillator",
+    "APO",
     "PPO",
     "DPO",
     "Coppock",

bindings/python/tests/test_known_values.py

@@ -66,6 +66,13 @@ def test_rsi_wilder_textbook_first_value():
     assert math.isclose(out[14], 70.464, abs_tol=0.05)
 
 
+def test_apo_constant_series_converges_to_zero():
+    # Both EMAs reproduce a constant exactly, so APO = 0 after warmup.
+    out = ta.APO(3, 5).batch(np.full(30, 42.0, dtype=np.float64))
+    assert np.all(np.isnan(out[:4]))
+    np.testing.assert_allclose(out[4:], 0.0, atol=1e-12)
+
+
 def test_macd_constant_series_converges_to_zero():
     out = ta.MACD().batch(np.full(200, 100.0))
     # Last row's MACD and signal must be ~0.

bindings/python/tests/test_new_indicators.py

@@ -51,6 +51,7 @@ SCALAR = [
     (ta.PMO, (35, 20)),
     (ta.StochRSI, (14, 14)),
     (ta.PPO, (12, 26)),
+    (ta.APO, (12, 26)),
     (ta.DPO, (20,)),
     (ta.Coppock, (14, 11, 10)),
     (ta.StdDev, (20,)),