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/t9_6_empty_state.stderr

@@ -0,0 +1,17 @@
+error: empty state `Empty`
+  --> tests/ui/t9_6_empty_state.rs:14:11
+   |
+14 |     state Empty {}
+   |           ^^^^^
+
+error[E0405]: cannot find trait `MActions` in this scope
+  --> tests/ui/t9_6_empty_state.rs:18:6
+   |
+18 | impl MActions for MActionContext<'_> {
+   |      ^^^^^^^^ not found in this scope
+
+error[E0425]: cannot find type `MActionContext` in this scope
+  --> tests/ui/t9_6_empty_state.rs:18:19
+   |
+18 | impl MActions for MActionContext<'_> {
+   |                   ^^^^^^^^^^^^^^ not found in this scope