feat: add Rust binary calculator example

First example of the binary server type — a compiled Rust MCP server
packaged as an MCPB. Based on the official Rust SDK calculator example
(rmcp 1.2.0, 2 tools: sum/sub, ~80 LOC).

Includes Cargo.toml, Dockerfile for Docker-based builds, .mcpbignore
to exclude source from the bundle, and README with build/pack/test
instructions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/calculator-rust/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "mcp-calculator"
+version = "1.0.0"
+edition = "2024"
+
+[dependencies]
+rmcp = { version = "1.2.0", features = ["server", "macros", "transport-io", "schemars"] }
+tokio = { version = "1", features = ["macros", "rt-multi-thread", "io-std"] }
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+anyhow = "1.0"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter", "std", "fmt"] }
+schemars = "1.0"
+
+[profile.release]
+strip = true
+lto = true