MAINT: Adjust type annotations in _rectangle.py

[postmeback]

The setters lower_left / lower_right / upper_left / upper_right are now consistent with the getters.

Closes #1842

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (7b357c7) 92.83% compared to head (91aba9e) 92.83%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1920   +/-   ##
=======================================
  Coverage   92.83%   92.83%           
=======================================
  Files          34       34           
  Lines        7058     7058           
  Branches     1389     1389           
=======================================
  Hits         6552     6552           
  Misses        359      359           
  Partials      147      147           

Impacted Files	Coverage Δ
pypdf/generic/_rectangle.py	100.00% <100.00%> (ø)

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[MartinThoma]

Well done, congratulations to your first merged PR! The update will go life latest on Sunday in the next release.

If you want, I can add you to https://pypdf.readthedocs.io/en/latest/meta/CONTRIBUTORS.html

[MartinThoma]

You might have noticed a few adjustments I made in this PR:

• The title: The prefix "MAINT" makes sure it gets recognized by https://github.com/py-pdf/pypdf/blob/main/make_changelog.py . The rest of the line should be something that would speak for itself within the changelog.
• The body: The "closes API inconsistency in RectangleObject? #1842" makes sure that the issue is closed with this PR once it got merged. That forms a link which others might find valuable. The rest of the body summarizes the outcome of the discussions in the issue.

The title of the PR typically becomes the first line in the squashed commit message. The body becomes the rest of the commit message.

[postmeback]

Sure, please add me. @MartinThoma