The manifest of PTC-Lisp builtin bindings exposed by the Runtime subsystem.
Owns the flat {name, binding} table that maps builtin names to their
&Runtime.* implementations. PtcRunner.Lisp.Env consumes bindings/0 to
build the initial environment, keeping Env decoupled from the Runtime
facade.
Binding tuple shapes are documented in PtcRunner.Lisp.Env.