Better handling of text overflow in FPDF.write() & FPDF.write_html() - fix #847

[Lucas-C]

This PR also silence warnings in test/text/test_unbreakable.py by moving the with pytest.warns() block at the correct indentation level

[stenci]

I tested these changes with my tests, and the result is now correct. I don't see any empty lines.

I'm not familiar with github, I don't know if it would be possible to pip install this branch, or to clone and use this in some way in my environment. I manually applied the same changes that I saw in this diff to the source code installed by pip on my environment and ran my own tests.

[gmischler]

I Don't remember the exact details of why we introduced the wordsplit argument back then. But if we can get rid of it again then that visibly simplifies the code.

I see that test/text/write_soft_hyphen.pdf now wraps one line a bit later than before. Any idea why (or why it didn't do that before)? I hope we're not overshooting the boundaries there now. In a few other test files I've drawn vertical lines at the boundaries or painted the background yellow to explicitly show we're staying within. Maybe we should do that here as well to be sure.

old:

new:

[Lucas-C]

I see that test/text/write_soft_hyphen.pdf now wraps one line a bit later than before. Any idea why (or why it didn't do that before)? I hope we're not overshooting the boundaries there now. In a few other test files I've drawn vertical lines at the boundaries or painted the background yellow to explicitly show we're staying within. Maybe we should do that here as well to be sure.

Yes I'm well aware of that 😊
I added an explanatory comment in this PR to explain that and keep a trace of this change of behaviour:
https://github.com/PyFPDF/fpdf2/blob/issue-847/test/text/test_write.py#L20

I think the idea at the time for this wordsplit argument was to avoid word-splitting in this particular case of calling FPDF.write() really close to the right edge of the page.

As this is the only reference PDF file in our test suite that is impacted by this change,
I think it's worth it. I'm going to merge this PR now.