feat: trade-flow microstructure indicators (part 2 of 4) (#113)

* feat(core): add 3 trade-flow microstructure indicators

SignedVolume (per-trade size signed by aggressor), CumulativeVolumeDelta
(running signed-volume total), and TradeImbalance (rolling buy/sell volume
imbalance over a trade window). All consume the Trade type, with full unit
coverage. Extends the Microstructure family.

* feat(bindings): expose trade-flow microstructure indicators

Python, Node and WASM bindings for SignedVolume, CumulativeVolumeDelta and
TradeImbalance. Each takes a trade via update(price, size, is_buy); Python and
Node expose a batch over three parallel arrays, WASM exposes per-trade update.
Regenerates node index.d.ts/.js.

* test(bindings,fuzz,bench): cover trade-flow microstructure indicators

Python and Node: reference values, streaming-vs-batch, lifecycle/repr and input
validation (zero window, negative size, non-positive price, mismatched batch
lengths). New indicator_update_trade fuzz target. Synthetic trade-tape benches
(signed_volume cheapest, trade_imbalance windowed/expensive).

* docs: add trade-flow indicators + bump counter to 227

README Microstructure family row gains signed volume / CVD / trade imbalance and
the counter goes 224 -> 227; CHANGELOG records the trade-flow indicators.

bindings/python/tests/test_lifecycle.py

@@ -150,3 +150,25 @@ def test_orderbook_lifecycle():
 
 def test_orderbook_topn_repr():
     assert repr(ta.OrderBookImbalanceTopN(5)) == "OrderBookImbalanceTopN(levels=5)"
+
+
+def test_tradeflow_lifecycle():
+    for ind in [ta.SignedVolume(), ta.CumulativeVolumeDelta()]:
+        assert ind.warmup_period() == 1
+        assert not ind.is_ready()
+        ind.update(100.0, 1.0, True)
+        assert ind.is_ready()
+        ind.reset()
+        assert not ind.is_ready()
+
+
+def test_trade_imbalance_lifecycle_and_repr():
+    ti = ta.TradeImbalance(3)
+    assert ti.warmup_period() == 3
+    assert not ti.is_ready()
+    for _ in range(3):
+        ti.update(100.0, 1.0, True)
+    assert ti.is_ready()
+    ti.reset()
+    assert not ti.is_ready()
+    assert repr(ta.TradeImbalance(4)) == "TradeImbalance(window=4)"