initial commit: hsmc v0.2 with during: activities

Hierarchical statechart codegen for Rust with:
- during: activities for state-scoped concurrent I/O
- field-list borrowing (split-borrow inside the run loop)
- embassy-first async with tokio support
- STATE_CHART const for tooling/inspection
- examples: microwave, microwave_tui, embassy_full, during_radio

hsmc-macros/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "hsmc-macros"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+description = "Procedural macro implementation for the hsmc crate."
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = { version = "2", features = ["full", "extra-traits"] }
+quote = "1"
+proc-macro2 = "1"
+
+[dev-dependencies]
+trybuild = "1"
+hsmc = { path = "../hsmc" }