chore(deps): make Qt backend optional (#350)

* chore(deps): make Qt backend optional

TODO:
- [ ] Add relevant entry in CHANGELOG
- [ ] Update install documentation
- [ ] Make sure `manim-slides convert` can run without any Qt backend
- [ ] Make sure test suite works (partially) without any Qt backend
- [ ] Make sure we can import `manim_slides` without any Qt backend

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* chore(deps): some fixes but wip

* chore(docs): update

* chore(deps): support PyQt6

* chore(deps): make Qt backend optional

TODO:
- [ ] Add relevant entry in CHANGELOG
- [ ] Update install documentation
- [ ] Make sure `manim-slides convert` can run without any Qt backend
- [ ] Make sure test suite works (partially) without any Qt backend
- [ ] Make sure we can import `manim_slides` without any Qt backend

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* chore(deps): some fixes but wip

* chore(docs): update

* chore(deps): support PyQt6

* fix(deps): ci and docs

* fix(lib): missing package

* chore(ci): does it work?

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* chore(test): skip failing

* chore(docs): update

* chore(docs): update

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix(docs): typo

* fix(test): quit instead of shutdown

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

README.md

@@ -88,11 +88,15 @@ manim-slides render example.py BasicExample
 # or use ManimGL
 manim-slides render --GL example.py BasicExample
 ```
+<!-- end usage -->
 
 > [!NOTE]
-> Using `manim-slides render` makes sure the use the `manim`
-> (or `manimlib`) library that was installed in the Python same environment.
-> Put simply, this is a wrapper of `manim render [ARGS]...` (or `manimgl [ARGS]...`).
+> Using `manim-slides render` makes sure to use the `manim`
+> (or `manimlib`) library that was installed in the same Python environment.
+> Put simply, this is a wrapper around
+> `manim render [ARGS]...` (or `manimgl [ARGS]...`).
+
+<!-- start more-usage -->
 
 To start the presentation using `Scene1`, `Scene2` and so on, run:
 
@@ -106,7 +110,7 @@ In our example:
 manim-slides BasicExample
 ```
 
-<!-- end usage -->
+<!-- end more-usage -->
 
 <p align="center">
   <img alt="Example GIF" src="https://raw.githubusercontent.com/jeertmans/manim-slides/main/static/example.gif">