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.

src/lib.rs

@@ -0,0 +1,39 @@
+//! # corex
+//!
+//! Resource-aware abstractions for async I/O, heavy compute, and
+//! background queue management, built on a single lazily-initialized
+//! global engine context.
+//!
+//! Call [`init`] once at startup (or simply let the first call to any
+//! entry point below trigger it lazily) and then use whichever of the
+//! feature-gated entry points your workload needs:
+//!
+//! - [`spawn_io`] (feature `io`) — spawn an async I/O task, tracing-instrumented.
+//! - [`compute`] (feature `compute`) — run CPU-bound work on a sized Rayon pool, panic-isolated.
+//! - [`spawn_bg`] (feature `bg`) — spawn a background task under bounded concurrency.
+//!
+//! Enable the `full` feature to pull in all three at once.
+
+pub use corex_core::context::{context, EngineContext};
+
+#[cfg(feature = "compute")]
+pub use corex_core::error::CorexError;
+
+#[cfg(feature = "io")]
+pub use corex_core::io::spawn_io;
+
+#[cfg(feature = "compute")]
+pub use corex_core::compute::compute;
+
+#[cfg(feature = "bg")]
+pub use corex_core::bg::spawn_bg;
+
+/// Bootstraps the global corex [`EngineContext`].
+///
+/// See [`corex_core::context::init`] for full semantics: this is safe to
+/// call any number of times, from any thread, and is equivalent to letting
+/// the first call to [`spawn_io`], [`compute`], or [`spawn_bg`] trigger
+/// initialization implicitly.
+pub fn init() -> &'static EngineContext {
+    corex_core::context::init()
+}