move parameters enums as separate headers

[piallai]

• rng_type_t, sample_method_t, schedule_t, sd_type_t can be included without including the whole stable-diffusion.h file
• SDMode and SDParams are set in separate headers to highlight the main parameters of the API

[leejet]

Thank you for your contribution. But as a C-style api header file, stable-diffusion.h should be kept as simple as possible, using only one file, so I don't think these changes are necessary.