Added integration and differenciation

[AadiVN]

Description

Ive added a working implementation of both integration and differenciation into the existing keyboard. The ui seems a bit squished but i didnt want to add a new page. However it does fail in expression conversion simply becuase i didnt want to edit that code.

Related issues & PRs

Its related to this issue

Checklist

Remove If [...] items that do not apply to your PR.

• I have made myself familiar with the CaTeX
  contributing guide.
• [x ] I added a PR description.
• [ x] I linked all related issues and PRs I could find (no links if there are none).
• If this PR changes anything about the main math_keyboard or example package
  (also README etc.), I created an entry in CHANGELOG.md (## UPCOMING RELEASE if the change
  on its own is not worth an update).
• If this PR includes a notable change in the math_keyboard package, I updated the version
  according to Dart's semantic versioning.
• If there is new functionality in code, I added tests covering all my additions.
• All required checks pass.

[github-actions]

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