replace `sprintf` in H3Index.c `h3ToString()`

[dcooley]

H3Index.c uses sprintf, but this won't pass R Checks (as of R 4.3)

checking compiled code ... WARNING
  File ‘h3lib/libs/h3lib.so’:
    Found ‘_sprintf’, possibly from ‘sprintf’ (C)
      Object: ‘h3Index.o’
  
  Compiled code should not call entry points which might terminate R nor
  write to stdout/stderr instead of to the console, nor use Fortran I/O
  nor system RNGs nor [v]sprintf.

Reference - https://www.tidyverse.org/blog/2023/03/cran-checks-compiled-code/#warning-regarding-the-use-of-codesprintfcode-in-cc

The solution is to use snprintf()

But this means we need to update the H3 source code directly.

• Make a PR into H3?
• Update it locally, plus our update script?

[dcooley]

linked issue - uber/h3#774

[dcooley]

I think our best option is to

• update h3Index.c to fail

    //sprintf(str, "%" PRIx64, h);
    //return E_SUCCESS;
    return E_FAILED;

• remove h3ToString from init.c
• Implement our own version in h3r

SEXP h3ToSexpString(H3Index h3) {
  char str[17];
  //h3ToString(h3, str, sizeof(str));
  int res = snprintf(str, sizeof(str), "%" PRIx64, h3);
  return Rf_mkChar(str);
}