[Flaw] Improve Import epub “loading screen”

[Palloxin]

Describe your suggested feature

https://github.com/LNReader/lnreader/assets/75091899/bdef2984-4aa8-4615-9c26-ad875c2b39c6

You can noticed the response delay when i click on the EPUB, then a black screen appears, then wait, then it disappears when the import has been completed.

Other details

the epub has 2172 chapters.

Acknowledgements

• [X] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
• [X] I have written a short but informative title.
• [X] If this is an issue with a source, I should be opening an issue in the sources repository.
• [X] I have updated the app to version 1.1.18.
• [X] I will fill out all of the requested information in this form.