fix: correct residue_string expected type

[RubenChM]

Changed the declaration of residue_string from an array of pointers (char *[]) to a standard character buffer (char []) and remove the address-of operator (&) when passing the buffer to strcpy, resolving the compiler (GCC 15) error:

src/fparams.c: In function 'get_fpocket_args':
src/fparams.c:296:24: error: passing argument 1 of 'strcpy' from incompatible pointer type [-Wincompatible-pointer-types]
  296 |                 strcpy(&residue_string, pt);
      |                        ^~~~~~~~~~~~~~~
      |                        |
      |                        char * (*)[8000]
In file included from src/../headers/fparams.h:19,
                 from src/fparams.c:2:
/home/conda/feedstock_root/build_artifacts/fpocket_1765458334087/_build_env/x86_64-conda-linux-gnu/sysroot/usr/include/string.h:125:39: note: expected 'char * restrict' but argument is of type 'char * (*)[8000]'
  125 | extern char *strcpy (char *__restrict __dest, const char *__restrict __src)
      |                      ~~~~~~~~~~~~~~~~~^~~~~~
src/fparams.c:297:23: error: assignment to 'char *' from incompatible pointer type 'char **' [-Wincompatible-pointer-types]
  297 |                 rest2 = residue_string;
      |                       ^

The old implementation was working fine since we are pointing to the same spot in memory, but it was taking 8 times more space for the buffer.

This closes #164 and allows the conda-forge to rebuild without adding constrains to the compiler version.

[simonbray]

@pschmidtke could you have a look and merge? The conda-forge infrastructure is failing to build due to this issue, since it switched to gcc 14. Thanks :)