bottleneck in tar_outdated() with CAS

[wlandau]

With:

# _targets.R
library(targets)
repository <- tar_repository_cas_local()
list(
  tar_target(x, seq_len(1e4), repository = repository),
  tar_target(y, x, pattern = map(x), repository = repository)
)

and:

# R console
library(targets)
tar_make()
proffer::pprof(tar_outdated(callr_function = NULL))

I see:

targets could have a global cache to store the results of Base 64 decoding