Rename crate to mytheclipse and flatten workspace to single crate

- Rename corex -> mytheclipse (corex name taken on crates.io by an
  unrelated crate published by David-Kunz in 2023)
- Flatten corex + corex-core workspace into a single crate; all modules
  (context/error/io/compute/bg) now live directly under src/
- Update Cargo.toml metadata: real repo URL, docs.rs, author
- Update README, example, doc comments, tracing span names
- Fix CI: single package dry-run (corex-core no longer separate)
- Fix publish workflow: single cargo publish step

src/bg.rs

@@ -0,0 +1,53 @@
+//! Bounded-concurrency background task execution.
+
+use tracing::Instrument;
+
+use crate::context::context;
+
+/// Spawns `future` as a background task once a concurrency permit is
+/// available, returning its [`tokio::task::JoinHandle`].
+///
+/// At most [`crate::context::EngineContext::bg_concurrency`] background
+/// tasks run at any one time; awaiting `spawn_bg` blocks the caller until a
+/// slot frees up, which is what provides the bound. A task's permit is held
+/// for the task's full lifetime and released automatically when it
+/// completes.
+///
+/// Panic isolation is provided by Tokio itself: a panicking background task
+/// cannot crash the runtime or any sibling task, and is surfaced to the
+/// caller as `Err(JoinError)` when the returned handle is awaited, exactly
+/// as with [`crate::io::spawn_io`].
+///
+/// # Panics
+///
+/// Panics if called outside the context of a running Tokio runtime.
+pub async fn spawn_bg<F>(future: F) -> tokio::task::JoinHandle<F::Output>
+where
+    F: std::future::Future + Send + 'static,
+    F::Output: Send + 'static,
+{
+    let permit = context()
+        .bg_semaphore
+        .acquire()
+        .await
+        .expect("mytheclipse: bg semaphore closed unexpectedly");
+    let span = tracing::info_span!("mytheclipse_bg_task");
+    tokio::spawn(
+        async move {
+            let _permit = permit;
+            future.await
+        }
+        .instrument(span),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn spawn_bg_roundtrips_a_value() {
+        let handle = spawn_bg(async { 9u32 }).await;
+        assert_eq!(handle.await.unwrap(), 9);
+    }
+}