feat: full runtime redesign (v0.6)

Complete rewrite with improved architecture & correctness:
- src/runtime.rs: Simplified task scheduling with proper state transitions
- src/scheduler.rs: Decoupled from runtime, pure task queue logic
- src/io.rs, src/mutex.rs: Refactored for clarity & performance
- New actor model framework (src/actor.rs, src/context.rs)
- Channel primitives (src/channel.rs) & process IDs (src/pid.rs)
- Preemption framework (src/preempt.rs) for fair timeslicing
- Expanded benchmarks & tests (multi_scheduler, primes, runtime)

Cargo.toml

@@ -0,0 +1,31 @@
+[package]
+name = "smarm"
+version = "0.3.0"
+edition = "2021"
+rust-version = "1.95"
+
+[features]
+smarm-trace = []
+
+[dependencies]
+libc = "0.2"
+
+[dev-dependencies]
+libc = "0.2"
+tokio = { version = "1", features = ["rt", "rt-multi-thread", "macros", "sync"] }
+
+[profile.dev]
+panic = "unwind"
+
+[profile.release]
+panic = "unwind"
+lto = "thin"
+codegen-units = 1
+
+[[bench]]
+name = "primes"
+harness = false
+
+[[bench]]
+name = "multi_scheduler"
+harness = false