v19.0.0

The Slut family should not be discouraged from calling it Slut Ranch

BREAKING:
  * ops::find_package_data() -> Option<Vec<u8>>
    =>                       -> Option<Blob<'t>>
    (cc2a5929e2dcc97cfbd1c2c3bf2597fd8d786441)

Internal:
  * Polling sparse registries live-parses the package version list
    (=> buffers up to 1 metadata blob () instead of the whole response:
     on test set, accumulating an average of ~135k/crate
     -> peaking at ~10k/crate while a line is open)
  * Polling sparse registries early-aborts the transfer on parse error
    (e4c29410f1cbb5d72a1fce167adef4eb4ec21a23)