Add corex library with resource-aware execution primitives

- Implement CI workflow for formatting, linting, testing, and documentation checks.
- Create publish workflow for automated publishing to crates.io.
- Add .gitignore to exclude build artifacts and editor files.
- Define Cargo.toml for corex and corex-core with dependencies and metadata.
- Add README.md files for corex and corex-core with usage instructions and licensing.
- Implement core execution primitives: spawn_io, compute, and spawn_bg with panic isolation.
- Establish global engine context for resource management based on logical CPU cores.
- Introduce error handling for compute panics.

examples/main.rs

@@ -0,0 +1,41 @@
+//! Demonstrates `corex`'s three execution primitives end to end, including
+//! automatic recovery from a panicking compute closure.
+
+#[tokio::main]
+async fn main() {
+    tracing_subscriber::fmt::init();
+
+    let ctx = corex::init();
+    println!(
+        "engine context: io_threads={} compute_threads={} bg_concurrency={}",
+        ctx.io_threads, ctx.compute_threads, ctx.bg_concurrency
+    );
+
+    let io_handle = corex::spawn_io(async {
+        tokio::time::sleep(std::time::Duration::from_millis(50)).await;
+        42u64
+    });
+
+    let sum_result = corex::compute(|| (1..=1_000u64).sum::<u64>());
+
+    let panic_result: Result<u64, corex::CorexError> = corex::compute(|| {
+        panic!("intentional panic to demonstrate isolation");
+    });
+
+    let recovery_result = corex::compute(|| 2u64 + 2u64);
+
+    let bg_handle = corex::spawn_bg(async {
+        tokio::time::sleep(std::time::Duration::from_millis(10)).await;
+        "bg-task-done"
+    })
+    .await;
+
+    let io_value = io_handle.await.expect("io task panicked");
+    let bg_value = bg_handle.await.expect("bg task panicked");
+
+    println!("spawn_io result: {io_value}");
+    println!("compute sum result: {sum_result:?}");
+    println!("compute panic-isolation result: {panic_result:?}");
+    println!("compute pool still usable after panic: {recovery_result:?}");
+    println!("spawn_bg result: {bg_value}");
+}