fix sum rcpp error on Unix systems (cpp11test)

[pachadotdev]

In #419, @nunotexbsd discovered that the Rcpp sum function fails in the cpp11test package. In any case, cpp11 can be installed from github without problem, it is just the R CMD check that does not like a missed Rcpp in imports.

I just verified that after installing cpp11 from main, I had to add Rcpp to imports.

In addition, I fixed some notes and the only remaining notes in cpp11test are

── R CMD check results ─────────────────────────────────────────────────────────────── cpp11test 0.0.0.9000 ────
Duration: 1m 19.3s

❯ checking for missing documentation entries ... WARNING
  Undocumented code objects:
    ‘_cpp11test_cpp11_add_vec_for_’ ‘_cpp11test_cpp11_insert_’
    ‘_cpp11test_cpp11_push_and_truncate_’ ‘_cpp11test_cpp11_release_’
    ‘_cpp11test_cpp11_safe_’ ‘_cpp11test_data_frame_’ ‘_cpp11test_grow_’
    ‘_cpp11test_protect_many_’ ‘_cpp11test_protect_many_cpp11_’
    ‘_cpp11test_protect_many_preserve_’ ‘_cpp11test_protect_many_rcpp_’
    ‘_cpp11test_protect_many_sexp_’ ‘_cpp11test_protect_one_’
    ‘_cpp11test_protect_one_cpp11_’ ‘_cpp11test_protect_one_preserve_’
    ‘_cpp11test_protect_one_sexp_’ ‘_cpp11test_rcpp_grow_’
    ‘_cpp11test_rcpp_push_and_truncate_’ ‘_cpp11test_rcpp_release_’
    ‘_cpp11test_rcpp_sum_dbl_accumulate_’ ‘_cpp11test_rcpp_sum_dbl_for_’
    ‘_cpp11test_rcpp_sum_dbl_foreach_’ ‘_cpp11test_rcpp_sum_int_for_’
    ‘_cpp11test_string_proxy_assignment_’ ‘_cpp11test_string_push_back_’
    ‘_cpp11test_sum_dbl_accumulate2_’ ‘_cpp11test_sum_dbl_accumulate_’
    ‘_cpp11test_sum_dbl_for2_’ ‘_cpp11test_sum_dbl_for3_’
    ‘_cpp11test_sum_dbl_for_’ ‘_cpp11test_sum_dbl_foreach2_’
    ‘_cpp11test_sum_dbl_foreach_’ ‘_cpp11test_sum_int_accumulate_’
    ‘_cpp11test_sum_int_for2_’ ‘_cpp11test_sum_int_for_’
    ‘_cpp11test_sum_int_foreach_’ ‘cpp11_add_vec_for_’ ‘cpp11_insert_’
    ‘cpp11_push_and_truncate_’ ‘cpp11_release_’ ‘cpp11_safe_’
    ‘data_frame_’ ‘grow_’ ‘protect_many_’ ‘protect_many_cpp11_’
    ‘protect_many_preserve_’ ‘protect_many_rcpp_’ ‘protect_many_sexp_’
    ‘protect_one_’ ‘protect_one_cpp11_’ ‘protect_one_preserve_’
    ‘protect_one_sexp_’ ‘rcpp_grow_’ ‘rcpp_push_and_truncate_’
    ‘rcpp_release_’ ‘rcpp_sum_dbl_accumulate_’ ‘rcpp_sum_dbl_for_’
    ‘rcpp_sum_dbl_foreach_’ ‘rcpp_sum_int_for_’
    ‘string_proxy_assignment_’ ‘string_push_back_’ ‘sum_dbl_accumulate2_’
    ‘sum_dbl_accumulate_’ ‘sum_dbl_for2_’ ‘sum_dbl_for3_’ ‘sum_dbl_for_’
    ‘sum_dbl_foreach2_’ ‘sum_dbl_foreach_’ ‘sum_int_accumulate_’
    ‘sum_int_for2_’ ‘sum_int_for_’ ‘sum_int_foreach_’
  All user-level objects in a package should have documentation entries.
  See chapter ‘Writing R documentation files’ in the ‘Writing R
  Extensions’ manual.

❯ checking installed package size ... NOTE
    installed size is 20.7Mb
    sub-directories of 1Mb or more:
      libs  20.6Mb