Append ESC + ENTER at end of commands sent to IPython shell

[Splines]

During testing in #109, we noticed that #18 is still not working on Windows machines, even with #81. I try to address the issue here again, with a solution inspired by this SO answer. I.e. we append ESC + ENTER to any command sent to an IPython shell, see the line:

// append ESC + ENTER to avoid IPython starting a multi-line input (#18)
command += "\x1b\x0d";

This seems to work in CI/CD based on this run on #109 that already has the changes of this PR merged.

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For reviewers on Windows machines @RickLuiken:

• please test that you can use the extension as usual, e.g. to preview cells.
• if this fix works: does it still work if you comment out these lines?

[Splines]

Note that the tests in this PR are not significant since we only introduce some relevant tests in #109.

[Splines]

Merging this to move on. However, I'm still particularly interested to know if this fix works for you even if you comment out these lines?

[RickLuiken]

Hi @Splines, I tested this with the latest commit and the latest manim version, it seems to still work! However, I tried also with commenting the lines you mentioned, and the fix did not work on this LaggyScene.