E16: add a cargo-fuzz harness

The repository had no fuzzing setup despite several natural targets —
the CSV parser, the Binance envelope deserializer, and the stateful
indicator/aggregator update paths.

Add a fuzz/ cargo-fuzz crate (detached from the workspace via its own
[workspace] table and the parent's exclude) with four targets:

- csv_reader      — CandleReader over arbitrary bytes
- binance_envelope — RawWsEnvelope deserialization from arbitrary strings
- indicator_update — RSI/EMA streaming + batch over arbitrary f64 series
- tick_aggregator — TickAggregator over arbitrary tick triples

Each target asserts the no-panic contract: malformed input must surface
as an Err. fuzz/README.md documents running them (nightly + cargo-fuzz).

Cargo.toml

@@ -8,7 +8,7 @@ members = [
     "bindings/wasm",
     "bindings/node",
 ]
-exclude = []
+exclude = ["fuzz"]
 
 [workspace.package]
 version = "0.1.4"