//! Physical operators for a small query-plan executor.
//!
//! Targeted scope:
//! - atom scans with repeated-variable filtering and variable-binding output
//! - semijoins
//! - natural joins
//!
//! The operators are intended to be composed by hand into a small plan and
//! evaluated against in-memory relations. Integration with an external query
//! plan IR is out of scope for this crate.