Function run 

pub fn run(body: impl FnOnce(Context))

Build and run a BDD test suite.

Works in both contexts:

• harness = false — parses CLI args for filtering/listing, calls std::process::exit on failure.
• #[test] functions — auto-detected via libtest-specific CLI args; skips arg parsing and panics on failure so other tests can still run.

Example

rsspec::run(|ctx| {
    ctx.describe("Calculator", |ctx| {
        ctx.it("adds", || { assert_eq!(2 + 3, 5); });
    });
});