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/node/__tests__/indicators.test.js

@@ -912,3 +912,42 @@ test('Doji signed mode encodes dragonfly/gravestone/neutral direction', () => {
   assert.equal(d.update(10, 12, 8, 10), 0); // long-legged -> neutral 0
   assert.equal(d.update(10, 12, 10, 12), 0); // not a doji -> 0
 });
+
+test('order-book indicators reference values', () => {
+  // Top-1: (3 - 1) / (3 + 1) = 0.5.
+  assert.equal(new wickra.OrderBookImbalanceTop1().update([100], [3], [101], [1]), 0.5);
+  // Top-2: bidDepth 3, askDepth 2 -> (3 - 2) / 5 = 0.2.
+  assert.ok(
+    Math.abs(new wickra.OrderBookImbalanceTopN(2).update([100, 99], [2, 1], [101, 102], [1, 1]) - 0.2) < 1e-12,
+  );
+  // Full: bidDepth 1, askDepth 3 -> -0.5.
+  assert.equal(new wickra.OrderBookImbalanceFull().update([100], [1], [101, 102], [2, 1]), -0.5);
+  // Microprice: (100*3 + 101*1) / 4 = 100.25.
+  assert.equal(new wickra.Microprice().update([100], [1], [101], [3]), 100.25);
+  // Quoted spread: 1 / 100.5 * 10000 ≈ 99.5025 bps.
+  assert.ok(Math.abs(new wickra.QuotedSpread().update([100], [1], [101], [1]) - 99.50248756) < 1e-6);
+});
+
+test('order-book streaming update matches batch', () => {
+  const snaps = Array.from({ length: 30 }, (_, i) => ({
+    bidPx: [100, 99],
+    bidSz: [1 + (i % 5), 1],
+    askPx: [101, 102],
+    askSz: [1 + ((i + 1) % 3), 1],
+  }));
+  const batch = new wickra.Microprice().batch(snaps);
+  const streamer = new wickra.Microprice();
+  assert.equal(batch.length, snaps.length);
+  for (let i = 0; i < snaps.length; i++) {
+    const s = streamer.update(snaps[i].bidPx, snaps[i].bidSz, snaps[i].askPx, snaps[i].askSz);
+    assert.ok(Math.abs(s - batch[i]) < 1e-12, `mismatch at ${i}: ${s} vs ${batch[i]}`);
+  }
+});
+
+test('order-book TopN rejects zero levels', () => {
+  assert.throws(() => new wickra.OrderBookImbalanceTopN(0));
+});
+
+test('order-book update rejects a crossed book', () => {
+  assert.throws(() => new wickra.QuotedSpread().update([102], [1], [101], [1]));
+});