feat: order-book microstructure indicators (part 1 of 4) (#112)

* feat(core): add microstructure input types (OrderBook, Trade, TradeQuote)

New non-OHLCV value types for the order-book / trade-flow indicator family:
Level, OrderBook (sorted, uncrossed depth snapshot), Side, Trade (with
aggressor side), and TradeQuote (trade paired with prevailing mid). Each has a
validating constructor plus a new_unchecked hot-path constructor, with full
unit coverage. Adds InvalidOrderBook / InvalidTrade error variants.

* feat(core): add 5 order-book microstructure indicators

OrderBookImbalanceTop1/TopN/Full (signed depth imbalance), Microprice
(size-weighted fair value), and QuotedSpread (top-of-book spread in bps). All
consume the OrderBook snapshot type, emit f64, are stateless and ready after
the first snapshot, with full unit coverage. Registers a new Microstructure
family in the taxonomy.

* feat(bindings): expose order-book microstructure indicators

Python, Node, and WASM bindings for OrderBookImbalanceTop1/TopN/Full,
Microprice and QuotedSpread. Each takes a depth snapshot via four equal-length
(bid_px, bid_sz, ask_px, ask_sz) arrays. Python and Node expose a batch over a
list of snapshots; WASM exposes per-snapshot update (the streaming model that
fits a browser book feed). Regenerates node index.d.ts/.js and registers the
new InvalidOrderBook/InvalidTrade arms in the Python error mapping.

* test(bindings,fuzz): cover order-book microstructure indicators

Python: smoke, reference values, streaming-vs-batch, lifecycle/repr and input
validation (mismatched lengths, crossed book, misordered levels, zero levels)
for all five order-book indicators. Node: reference values, streaming-vs-batch,
and rejection cases. Adds an indicator_update_orderbook fuzz target driving
every order-book indicator over arbitrary (incl. degenerate) snapshots.

* bench(microstructure): synthetic order-book benchmarks

Add a bench_orderbook_input harness and synthesise a five-level book around
each candle close (no order-book dataset ships with the repo). Benches the
cheapest (top-of-book imbalance) and most-expensive (full-depth imbalance) plus
microprice, matching the curated cheapest/expensive-per-family approach.

* docs: add Microstructure family + bump indicator counter to 224

README gains the Microstructure family row (order-book imbalance, microprice,
quoted spread) and the indicator counter goes 219 -> 224 across seventeen
families; CHANGELOG records the new order-book indicators and value types.

bindings/python/tests/test_known_values.py

@@ -847,3 +847,26 @@ def test_doji_signed_dragonfly_gravestone_neutral():
     assert d.update((10.0, 12.0, 8.0, 10.0, 1.0, 2)) == pytest.approx(0.0)
     # A large body is not a doji at all -> 0 regardless of position.
     assert d.update((10.0, 12.0, 10.0, 12.0, 1.0, 3)) == pytest.approx(0.0)
+
+
+def test_orderbook_imbalance_reference_values():
+    # Top-1: (3 - 1) / (3 + 1) = 0.5.
+    assert ta.OrderBookImbalanceTop1().update([100.0], [3.0], [101.0], [1.0]) == pytest.approx(0.5)
+    # Top-2: bidDepth 3, askDepth 2 -> (3 - 2) / 5 = 0.2.
+    topn = ta.OrderBookImbalanceTopN(2)
+    assert topn.update([100.0, 99.0], [2.0, 1.0], [101.0, 102.0], [1.0, 1.0]) == pytest.approx(0.2)
+    # Full: bidDepth 1, askDepth 3 -> (1 - 3) / 4 = -0.5.
+    full = ta.OrderBookImbalanceFull()
+    assert full.update([100.0], [1.0], [101.0, 102.0], [2.0, 1.0]) == pytest.approx(-0.5)
+
+
+def test_microprice_reference_value():
+    # (100*3 + 101*1) / (1 + 3) = 401 / 4 = 100.25 — heavy ask pulls toward bid.
+    mp = ta.Microprice()
+    assert mp.update([100.0], [1.0], [101.0], [3.0]) == pytest.approx(100.25)
+
+
+def test_quoted_spread_reference_value():
+    # spread 1.0, mid 100.5 -> 1 / 100.5 * 10_000 ≈ 99.5025 bps.
+    qs = ta.QuotedSpread()
+    assert qs.update([100.0], [1.0], [101.0], [1.0]) == pytest.approx(99.50248756, abs=1e-6)