fix: missing argument names in rb_prohibit_copy (build failure on older GCC/Clang)

[flfymoss]

The argument variable names of rb_prohibit_copy introduced in #98 are missing.
This is C23-style function declarations (N2480), so it causes build failures on older versions of GCC <= 10 (and Clang <= 10) ¹ with the following error:

compiling main.c
compiling skippable_frame.c
compiling streaming_compress.c
compiling streaming_decompress.c
compiling zstdruby.c
zstdruby.c: In function ‘rb_prohibit_copy’:
zstdruby.c:277:31: error: parameter name omitted
  277 | static VALUE rb_prohibit_copy(VALUE, VALUE)
      |                               ^~~~~
zstdruby.c:277:38: error: parameter name omitted
  277 | static VALUE rb_prohibit_copy(VALUE, VALUE)
      |                                      ^~~~~
make: *** [Makefile:248: zstdruby.o] Error 1

make failed, exit code 2

Although this error does not occur on recent versions of GCC/Clang, it may cause build failures in slightly older environments.
This PR fixes the function declaration by explicitly specifying the argument variable names to maintain compatibility.

Footnotes

1. https://en.cppreference.com/w/c/23 ↩