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.

.gitignore

@@ -0,0 +1,15 @@
+# Cargo build artifacts
+/target
+/crates/*/target
+
+# corex is a library workspace: the lockfile is not committed, per Rust's
+# convention for libraries (binaries/applications should commit theirs).
+# Cargo regenerates it locally and in CI on every build.
+Cargo.lock
+
+# Editor / OS noise
+.DS_Store
+Thumbs.db
+*.swp
+.idea/
+.vscode/