Fix telemetry feature build

[TLmaK0]

Summary

• Update rusty_dashed to git master (replaces iron/hyper with tiny_http + rust-embed, removes rustc-serialize)
• Replace extern crate serde_derive with serde::Serialize derive path
• Telemetry feature now compiles and works on modern Rust

Test plan

• cargo build --features telemetry compiles
• cargo test --release passes
• Manual test: function_approximation with telemetry dashboard works