Rework rawsave and add rawsave_target

[akash-akya]

Fixes #3941

[akash-akya]

@jcupitt need your help to review the changes.

I kept vips_rawsave_fd function but removed rawsave_fd operation in favor of rawsave_target. I am not sure if this breaks something in the downstream. Do we have to retain the operation?

How to regenerate doc/function-list.xml file?

[jcupitt]

It's probably OK to remove rawsave_fd, I doubt if anyone was using it. We'll need to keep the C API point vips_rawsave_fd() to avoid link failures, but we can tag it as deprecated.

You need gen-function-list.py in the doc/ directory.

I'll do a very quick review for you.

[jcupitt]

Looks fine, other than one small thing. Nice!

[jcupitt]

We could maybe add a _buffer subclass too, for completeness.

[akash-akya]

Facing an issue with generating the docs. I am not able to install pyvips due to compilation issue. I think my local env is messed up because of multiple vips I have installed

 build/temp.macosx-14.3-x86_64-cpython-312/_libvips.c:6208:27: error: incompatible function pointer types passing 'void (*)(void *)' to parameter of type 'VipsCallbackFn' (aka 'int (*)(void *, void *)') [-Wincompatible-function-pointer-types]
        vips_value_set_blob(x0, x1, x2, x3);

---

Added vips_rawsave_buffer. So vips_rawsave_buffer is very similar to vips_image_write_to_memory but only added for completeness sake correct?

[akash-akya]

Hi @jcupitt, can you take a look at this? Thanks

[jcupitt]

Sorry, I was distracted on other projects, I'll reread this now.

[jcupitt]

It looks great! Thank you for doing this work, @akash-akya!