Added some type stubs to core.pyi.

To let Pylance stop warning me that these methods doesn't exist.

name: Pull Request
about: Propose changes to the codebase
title: '[PR] Add method signatures to request methods'
labels: ''
assignees: ''

Related Issue
#319 Although it's fixed, I think this is the best way to solve it.

Proposed Changes
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Types of changes
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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist
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• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I am aware that this is an nbdev project, and I have edited, cleaned, and synced the source notebooks instead of editing .py or .md files directly.

Additional Information
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