value-graph 0.1.0: JSON-free, bigint-free binary snapshot layer

- src/snapshot.js: compact portable wire (VGST store / VGGP graph), binary maps for
  params/pattern/objects (no JSON), buffer values (no JS bigint), CRC-32 guarded.
- createFileStore: binary per-key files (encodeEntryBytes/decodeEntryBytes).
- ValueGraph snapshot/snapshotFile/restore/loadFile; keys base64url(params-bytes).
- 60 tests (node:test + rigor incl. 'flip ANY byte never decodes silently').

bench/hotpath.js

@@ -0,0 +1,38 @@
+// Hotpath micro-benchmark: how fast is a value-graph `get` on the authorization
+// hotpath? Compared against a plain Map lookup.
+import { performance } from 'node:perf_hooks';
+import { ValueGraph } from '../src/index.js';
+
+function bench(name, fn, iterations = 200_000) {
+  for (let i = 0; i < 10_000; i++) fn(); // warmup
+  const t0 = performance.now();
+  for (let i = 0; i < iterations; i++) fn();
+  const ms = performance.now() - t0;
+  const nsPerOp = (ms * 1e6) / iterations;
+  const opsPerSec = Math.round((iterations / ms) * 1000);
+  console.log(`${name.padEnd(46)} ${nsPerOp.toFixed(0).padStart(8)} ns/op   ${String(opsPerSec).padStart(10)} ops/sec`);
+}
+
+const vg = new ValueGraph();
+vg.compute('balance', () => 1250);
+await new Promise((res) => vg.get('u:1', 'balance', {}, (e, v) => res(v)));
+const plan = vg.plan('u:1', 'balance', {}); // cached plan for the hot loop
+
+const coldVg = new ValueGraph();
+coldVg.compute('balance', () => 42);
+
+vg.define('a', { operator: 'source', fn: () => 10 });
+vg.define('b', { operator: 'source', fn: () => 20 });
+vg.define('c', { operator: 'source', fn: () => 30 });
+vg.define('risk', { operator: 'fusion:custom', parents: ['a', 'b', 'c'], weights: [0.6, 0.3, 0.1] });
+await new Promise((res) => vg.get('u:1', 'risk', {}, (e, v) => res(v)));
+
+const baseline = new Map([['u:1|balance|{}', 1250]]);
+
+console.log('--- hotpath (authorization value lookup) ---');
+bench('Map.get baseline', () => baseline.get('u:1|balance|{}'));
+bench('vg.get cached (plan/run)', () => vg.run(plan, () => {}));
+bench('vg.get cached (get + compile)', () => vg.get('u:1', 'balance', {}, () => {}));
+bench('vg.get cold (fresh compute)', () => coldVg.get('x', 'balance', {}, () => {}));
+bench('vg.get fusion:custom DAG', () => vg.get('u:1', 'risk', {}, () => {}));
+bench('vg.query duplex {get}', () => { const q = vg.query('u:1', 'balance', {}); q.sink.write({ get: true }); q.sink.end(); });