Create agreement between argument type and format string

[jennybc]

Please correct before 2023-12-10 to safely retain your package on CRAN.

The relevant warning can be seen in GHA:

── R CMD check ─────────────────────────────────────────────────────────────────
* using log directory ‘/home/runner/work/vroom/vroom/check/vroom.Rcheck’
* using R Under development (unstable) (2023-11-26 r8[56](https://github.com/tidyverse/vroom/actions/runs/7021455235/job/19103553319#step:7:58)38)
* using platform: x86_64-pc-linux-gnu
* R was compiled by
    gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
    GNU Fortran (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
* running under: Ubuntu 22.04.3 LTS
* using session charset: UTF-8
* using options ‘--no-manual --as-cran’
* checking for file ‘vroom/DESCRIPTION’ ... OK
* this is package ‘vroom’ version ‘1.6.4.9000’
* package encoding: UTF-8
* checking package namespace information ... OK
* checking package dependencies ... OK
* checking if this is a source package ... OK
* checking if there is a namespace ... OK
* checking for executable files ... OK
* checking for hidden files and directories ... OK
* checking for portable file names ... OK
* checking for sufficient/correct file permissions ... OK
* checking whether package ‘vroom’ can be installed ... [61s/[59](https://github.com/tidyverse/vroom/actions/runs/7021455235/job/19103553319#step:7:61)s] WARNING
Found the following significant warnings:
  vroom_big_int.h:59:30: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_chr.h:41:26: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_dttm.h:[68](https://github.com/tidyverse/vroom/actions/runs/7021455235/job/19103553319#step:7:70):27: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_date.h:50:27: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_dbl.h:40:26: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_fct.h:125:29: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_int.h:38:26: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_num.h:50:26: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_time.h:50:27: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_rle.h:43:26: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘R_xlen_t’ {aka ‘long int’} [-Wformat=]
  vroom_write.cc:2[73](https://github.com/tidyverse/vroom/actions/runs/7021455235/job/19103553319#step:7:75):16: warning: field precision specifier ‘.*’ expects argument of type ‘int’, but argument 2 has type ‘std::vector<char>::size_type’ {aka ‘long unsigned int’} [-Wformat=]
See ‘/home/runner/work/vroom/vroom/check/vroom.Rcheck/00install.out’ for details.
* used C compiler: ‘gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0’
* used C++ compiler: ‘g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0’