Blocknote/version upgrade

[gyash1512]

This pull request updates the codebase to use the new insertOrUpdateBlockForSlashMenu API from @blocknote/core/extensions in place of the deprecated insertOrUpdateBlock for slash menu item insertions. It also updates BlockNote dependencies to version 0.46.2, ensuring compatibility with the latest API changes. Additionally, minor improvements are made to type safety and plugin extension access.

API Migration and Compatibility Updates:

• Replaced all uses of insertOrUpdateBlock with insertOrUpdateBlockForSlashMenu for slash menu actions in CodeBlock.tsx, getGeniusSlashMenuItems.ts, and getWhiteboardSlashMenuItems.tsx to align with the latest BlockNote API. [1] [2] [3] [4] [5] [6] [7] [8]
• Updated all BlockNote-related dependencies (@blocknote/core, @blocknote/react, @blocknote/mantine, @blocknote/xl-multi-column) to version 0.46.2 in package.json to ensure compatibility with the new API. [1] [2]

Code Quality and Type Safety:

• Improved type safety in CodeBlock.tsx by explicitly typing the content property as "none" as const.

Plugin Extension Handling:

• Updated access to the sideMenu extension in ColumnResizeExtension.ts to use getExtension("sideMenu") with optional chaining and type casting, improving robustness and future compatibility. [1] [2]

Miscellaneous:

• Bumped the package version to 1.0.20 in package.json.