jolt's `is` was a fixed macro with no assert-expr multimethod, and the runner
bypassed the report multimethod, so libraries couldn't register custom
assertions or custom report types (e.g. test.check's ::trial/::shrunk).
Add assert-expr (2-arg [msg form], dispatch on the form's first symbol /
:default / :always-fail), do-report routing through report, and report
:pass/:fail/:error methods that feed the counters. `is` dispatches to an
explicitly-registered assert-expr method before its inline path, so thrown?/
thrown-with-msg?/= and every built-in form stay byte-identical.
Runtime stdlib only, no re-mint. test/chez/clojure-test.clj self-checks the
extension points + full is/are/testing/thrown?/use-fixtures surface; smoke gate
runs it.
