test/atom: use correct format specifier for size_t

test/atom: use correct format specifier for size_t

From MSVC:

test\atom.c(98): note: consider using '%zu' in the format string
test\atom.c(98): warning C4477: 'fprintf' : format string '%lu' requires an argument of type 'unsigned long', but variadic argument 1 has type 'size_t'
test\atom.c(100): note: consider using '%zu' in the format string
test\atom.c(100): warning C4477: 'fprintf' : format string '%lu' requires an argument of type 'unsigned long', but variadic argument 1 has type 'size_t'
test\atom.c(114): note: consider using '%zu' in the format string
test\atom.c(114): warning C4477: 'fprintf' : format string '%lu' requires an argument of type 'unsigned long', but variadic argument 1 has type 'size_t'
test\atom.c(128): note: consider using '%zu' in the format string
test\atom.c(128): warning C4477: 'fprintf' : format string '%lu' requires an argument of type 'unsigned long', but variadic argument 1 has type 'size_t'
test\atom.c(130): note: consider using '%zu' in the format string
test\atom.c(130): warning C4477: 'fprintf' : format string '%lu' requires an argument of type 'unsigned long', but variadic argument 1 has type 'size_t'
test\atom.c(137): note: consider using '%zu' in the format string
test\atom.c(137): warning C4477: 'fprintf' : format string '%lu' requires an argument of type 'unsigned long', but variadic argument 2 has type 'size_t'

Signed-off-by: Ran Benita <ran@unusedvar.com>