[esp] Add Rust no-std example.

esp/rust/02_esp-gen-no-std/Cargo.toml

@@ -0,0 +1,30 @@
+[package]
+edition      = "2021"
+name         = "esp-gen-test"
+rust-version = "1.86"
+version      = "0.1.0"
+
+[[bin]]
+name = "esp-gen-test"
+path = "./src/bin/main.rs"
+
+[dependencies]
+esp-bootloader-esp-idf = { version = "0.2.0", features = ["esp32"] }
+esp-hal                = { version = "=1.0.0-rc.0", features = ["esp32"] }
+
+critical-section = "1.2.0"
+
+
+[profile.dev]
+# Rust debug is too slow.
+# For debug builds always builds with some optimization
+opt-level = "s"
+
+[profile.release]
+codegen-units    = 1     # LLVM can perform better optimizations using a single thread
+debug            = 2
+debug-assertions = false
+incremental      = false
+lto              = 'fat'
+opt-level        = 's'
+overflow-checks  = false