Simplify pypdfium2 use and avoid back-and-forth conversion

[mara004]

pypdfium2.render() outputs BGR by default and provides a to_numpy() function directly (zero-copy).
Disclaimer: untested, change made through GitHub's web interface

[CLAassistant]

All committers have signed the CLA.

[paddle-bot]

Thanks for your contribution!

[Bobholamovic]

Thanks for your contribution! Please make a pull request to the develop branch.

The base branch was changed.

[mara004]

I'm afraid your attempt to change the base branch has caused issues, seems like it pulled in a lot of unrelated commits.

I can try to fix this up sooner or later. Alternatively, feel free to integrate the change on your own.

[Bobholamovic]

I guess you should probably create your branch from the develop branch and re-make the commits.

[mara004]

Done, base is now develop cleanly.

[mara004]

GitHub really could be better at branch changes, because the same patch applies on both release/3.2 and develop, but nevermind...

[Bobholamovic]

LGTM