examples: move Rust examples into a top-level examples/rust/ crate

The three Rust examples (backtest, fetch_btcusdt, live_binance) used to
live each in their own crate's examples/ dir, splitting the example set
across crates and burying it inside the source tree. Move them into a new
workspace member crate at `examples/rust/` (package `wickra-examples`,
`publish = false`) so all language examples sit under one top-level
`examples/<lang>/` tree.

* `examples/rust/Cargo.toml` declares the per-binary deps (wickra,
  wickra-data with the `live-binance` feature always on, serde_json, tokio
  for the macro and current-thread runtime).
* `examples/rust/src/bin/{backtest,fetch_btcusdt,live_binance}.rs` are the
  three migrated binaries; their doc-comments and the fetch_btcusdt output
  path are updated for the new location and run command
  (`cargo run -p wickra-examples --bin <name>`).
* Workspace `Cargo.toml` lists the new member; the now-empty
  `[dev-dependencies]` extras (`wickra`, `tokio` in wickra-data and
  `serde_json` in wickra) that existed only for these examples are dropped.
* The `[[example]] live_binance` table is removed from wickra-data's
  manifest since the file moved out.
* README "Languages" + project-layout, examples/README.md, Quickstart-Rust
  and Data-Layer are pointed at the new paths and commands.

`cargo build -p wickra-examples` and `cargo run --release -p wickra-examples
--bin backtest -- examples/data/btcusdt-1d.csv` both succeed; the rest of
the workspace (core, data, wickra) builds, clippies (`--all-targets -D
warnings`) and tests (508 core + 28 data + 1 integration + 74+3+1
doctests) all stay green.

README.md

@@ -120,7 +120,7 @@ inherit it automatically.
 | Python (PyO3)     | `pip install wickra`                          | `examples/python/backtest.py` |
 | Node.js (napi-rs) | `npm install wickra`                          | `bindings/node/examples/backtest.js` |
 | Browser / WASM    | `npm install wickra-wasm`                     | `bindings/wasm/examples/index.html` |
-| Rust              | `cargo add wickra`                            | `crates/wickra/examples/backtest.rs` |
+| Rust              | `cargo add wickra`                            | `examples/rust/src/bin/backtest.rs` |
 
 Each binding ships several runnable examples (streaming, backtest, live feed);
 [`examples/README.md`](examples/README.md) is the full cross-language index.
@@ -182,23 +182,22 @@ A Python live-trading example using the public `websockets` package lives at
 wickra/
 ├── crates/
 │   ├── wickra-core/         core engine + all 71 indicators
-│   ├── wickra/              top-level facade crate (publishes on crates.io)
-│   │                        + benches/, examples/ (backtest, fetch_btcusdt)
-│   │                        and examples/data/ real BTCUSDT datasets
+│   ├── wickra/              top-level facade crate (publishes on crates.io) + benches/
 │   └── wickra-data/         CSV reader, tick aggregator, live exchange feeds
-│                            + examples/live_binance.rs
 ├── bindings/
 │   ├── python/              PyO3 + maturin (publishes on PyPI)
 │   ├── node/                napi-rs (publishes on npm) + examples/
 │   └── wasm/                wasm-bindgen (browsers, bundlers, Node) + examples/
 ├── examples/                examples/README.md indexes every language
+│   ├── data/                real BTCUSDT OHLCV datasets, one per timeframe
+│   ├── rust/                Rust workspace member (`wickra-examples`)
 │   └── python/              backtest, live trading, parallel assets, multi-tf
 └── .github/workflows/       CI and release pipelines
 ```
 
-Rust benchmarks and examples live inside their crate
-(`crates/wickra/benches/`, `crates/<name>/examples/`); there is no
-top-level `benches/` directory.
+Rust benchmarks live in `crates/wickra/benches/`; runnable Rust examples live
+in the workspace member crate at `examples/rust/`. There is no top-level
+`benches/` directory.
 
 ## Building everything from source