Move Rust examples into their crates so cargo publish picks them up

The previous `[[example]] path = "../../examples/rust/..."` entries
pointed at files outside the crate root. cargo only packages files
inside the crate directory, so the examples would have been silently
dropped on publish. Moving them to crates/wickra/examples/ and
crates/wickra-data/examples/ keeps them as part of the published
package and lets cargo discover them automatically (no [[example]]
override needed). README and project-layout section updated.

crates/wickra-data/Cargo.toml

@@ -41,5 +41,4 @@ tokio = { version = "1", features = ["macros", "rt-multi-thread"] }
 
 [[example]]
 name = "live_binance"
-path = "../../examples/rust/live_binance.rs"
 required-features = ["live-binance"]