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_streaming_vs_batch.py

@@ -217,3 +217,17 @@ def test_orderbook_streaming_matches_batch():
     streamer = ta.Microprice()
     streamed = np.array([streamer.update(*snap) for snap in snaps], dtype=np.float64)
     assert _equal_with_nan(batch, streamed)
+
+
+def test_tradeflow_streaming_matches_batch():
+    n = 30
+    price = np.full(n, 100.0)
+    size = np.array([1.0 + (i % 4) for i in range(n)], dtype=np.float64)
+    is_buy = [i % 3 != 0 for i in range(n)]
+    batch = ta.CumulativeVolumeDelta().batch(price, size, is_buy)
+    streamer = ta.CumulativeVolumeDelta()
+    streamed = np.array(
+        [streamer.update(price[i], size[i], is_buy[i]) for i in range(n)],
+        dtype=np.float64,
+    )
+    assert _equal_with_nan(batch, streamed)