Add method db_copy_to.Pool()

[mgirlich]

library(pool)
library(dplyr, warn.conflicts = FALSE)
library(dbplyr, warn.conflicts = FALSE)

conn <- dbPool(RSQLite::SQLite())
mt <- copy_to(conn, mtcars, "mtcars", temporary = FALSE)
auto_copy(mt, tibble(cyl = 3), copy = TRUE)
#> Error in UseMethod("db_copy_to"): no applicable method for 'db_copy_to' applied to an object of class "c('Pool', 'R6')"

^{Created on 2023-08-08 with reprex v2.0.2}

[hadley]

I've "fixed" this but it's not super satisfying because auto_copy() defaults to create temporary tables, which Pool doesn't support.