Use `deparse1` to avoid breaking lines in (error) messages

[klmr]

Error description

deparse returns vectors of length > 1 for long R expressions. This may break (or at least mangle) error messages produced by ‘box’.

For consistency, we should probably ban deparse from the code base entirely, and replace it with deparse1 (using a custom, vendored implementation to avoid depending on R 4.0.0).

R version

n/a

‘box’ version

1.1.2.9000