Handles both bare {fields, records} and the
{result: {fields, records}} wrapper shape.
Examples
tf <- tempfile(fileext = ".json")
writeLines('{"fields": [{"id": "a", "type": "int"}]}', tf)
res <- morie_arsau_read_sidecar(tf)
res$fields
#> [[1]]
#> [[1]]$id
#> [1] "a"
#>
#> [[1]]$type
#> [1] "int"
#>
#>
unlink(tf)
