feat: add preventAutoDelete method to ClassHandle

[marcosc90]

This PR adds .preventAutoDelete() method to allow users to explicitly prevent an object from being automatically deleted when .setAutoDeleteLater is set to true. This is quite useful when you need a long-lived handle and want to make sure it doesn't get auto-deleted with other short-lived handles.

const vips = await Vips(options);
vips.setAutoDeleteLater(true);
...
const im = vips.Image.newFromBuffer(u8);
im.preventAutoDelete();
...
const im2 = vips.Image.newFromBuffer(u8);
im2.resize(...).crop(...).gaussblur(...);

// deletes all 4 handles created by im2 chain
vips.flushPendingDeletes();

im.isDeleted(); // false
im.delete(); // when you're done

Without this method the current alternative if you needed a long-lived handle was to .setAutoDeleteLater(false) and call .deleteLater after each operation

const im2 = vips.Image.newFromBuffer(u8);
im2.deleteLater()
   .resize(...)
   .deleteLater()
   .crop(...)
   .deleteLater()
   .gaussblur(...)
   .deleteLater();

[kleisauke]

Great! I've made some minor improvements here:
denodeteam/wasm-vips@prevent-auto-delete...kleisauke:wasm-vips:prevent-auto-delete

(I was unable to push these changes directly to your PR, likely because the 'Allow edits and access to secrets by maintainers' option is disabled)

[marcosc90]

(I was unable to push these changes directly to your PR, likely because the 'Allow edits and access to secrets by maintainers' option is disabled)

Thanks! Couldn't find this setting on mobile (I'm flying back home) but managed to push your changes.

[kleisauke]

Thank you! This will be in v0.0.10.