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/tests/ui.rs

@@ -0,0 +1,8 @@
+//! Compile-fail tests for `statechart!` validations (§9.9) and
+//! compile-pass parse tests (spec §8).
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/ui/*.rs");
+    t.pass("tests/ui_pass/*.rs");
+}