The extendr crates have been bumped to 0.9.0, which drops the
R_NamespaceRegistry binding and clears the R CMD check NOTE "Found
non-API call to R: 'R_NamespaceRegistry'".
The package scaffolding now uses rextendr 0.5.0.
R/extendr-wrappers.R is generated during the build by a small document
binary (src/rust/document.rs), and src/entrypoint.c registers extendr's
panic hook.
inst/AUTHORS.md now credits the extendr and winnow crates, which
declare no authors field.