Add prerequisite installation instructions to all examples

[williamjameshandley]

Summary

• Added executable !pip install cells to all 18 example notebooks
• Added explanatory "Prerequisites" markdown headers before install cells
• Install cells include blackjax from the nested sampling fork and notebook-specific dependencies
• JAX is not explicitly installed (it's a blackjax dependency)
• Install cells are separate from import statements

Fixes #13

Changes

• Modified 18 notebooks across basic/, advanced/, physics/, sbi/, and integrations/ directories
• Each notebook now has:
  1. Title/header markdown
  2. Prerequisites markdown section
  3. Executable install cell with !pip install commands
  4. Rest of content

Test plan

• Verify notebooks display correctly in Jupyter Book build
• Confirm install commands work in notebook environments

🤖 Generated with Claude Code

[yallup]

Hard to give inline comments on ipynbs, good idea but some things missing:

• integration examples are missing or have malformed prerequisites
• One may be able to phrase the MD structure better, particularly in terms of how the sidebar toc picks things up, e.g. on the SBI example we have ## Prerequisites that then covers all the subsequent code that really should be under ## NSPosterior implementation. Prerequisites should be a lower indent level and the content should still be under the correct header.