AI Menu positioning when editing multiple blocks

Describe the bug
Originally described in https://github.com/TypeCellOS/BlockNote/pull/2247

Two issues:

• The AI Menu opens & attempts to scroll, it should be smarter about not doing this if it is already in view
• The AI Menu maybe should open relative to the blocks rather than relative to the text selection that the AI created, can be hard to review in context when the menu covers previous text

To Reproduce
<clear steps to reproduce are super helpful! Best is to provide an online sandbox, click to create one>

Misc

• Node version:
• Package manager:
• Browser:
• I'm a sponsor and would appreciate if you could look into this sooner than later 💖

Start by reviewing the behavior described in PR #2247 and reproducing the issue in examples/01-basic/01-minimal/App.tsx. Focus on the unresolved positioning concern: when editing multiple blocks, the AI Menu should remain useful for reviewing the affected text without covering previous context; the issue does not name an implementation file or test.