v0.1: green-thread actors, supervision, channels, benchmark

Hand-rolled context switching on mmap'd stacks with guard pages,
allocator-driven RDTSC preemption, unbounded MPSC channels, supervision
via per-slot Signal mailboxes, root supervisor as sentinel PID.

Lib + tests + benches clean check/clippy. All 29 tests pass.
Bench: smarm 3.4% over serial baseline, within 160us of tokio
current-thread on prime-counting fan-out.

Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "smarm"
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.95"
+
+[dependencies]
+libc = "0.2"
+
+[dev-dependencies]
+tokio = { version = "1", features = ["rt", "macros", "sync"] }
+
+[profile.dev]
+panic = "unwind"
+
+[profile.release]
+panic = "unwind"
+lto = "thin"
+codegen-units = 1
+
+[[bench]]
+name = "primes"
+harness = false