Use fread instead of arrow to get data in get_forecaster_predictions_alt

[nmdefries]

Description

Some submitted predictions have a column order that doesn't agree with the arrow schema specified in get_forecaster_predictions_alt. Due to a change in behavior in newer versions of arrow, the column order in input files and in the arrow schema must now be the same (previously were reordered). We pinned arrow to a working version as a patch, but that version is now quite old.

Incidentally, arrow is not providing much additional benefit, so we aren't tied to it. Since we want to prioritize speed, data.table::fread is a good alternative. data.table also offers opportunities for future optimization. Since fread can read from URL (downloads to a temp file), we don't need to do our own download step, which simplifies the process somewhat.

Fixes

Closes #609

[dshemetov]

Tested locally and works fine with the stated edge cases (forecasters that change their column order from date to date), e.g.:

evalcast:::get_forecaster_predictions_alt("COVIDhub_CDC-ensemble", forecast_dates = a
    s.Date(c("2021-11-08", "2021-11-15"))) %>% tibble

returns consistent and correct prediction cards.

[dshemetov]

Consider bumping the patch version on evalcast btw and adding a note in the CHANGELOG? Non-blocking.

[nmdefries]

@dshemetov Do you have merge ability? This is ready