fix(demos): port LIT integration demo model loading to TransformerBridge

[ZacharyZcR]

Description

In #1740 the imports in demos/LIT_Integration_Demo.ipynb were updated to TransformerBridge, but the model loading cell still called HookedTransformer.from_pretrained(...). Because HookedTransformer was no longer imported, running that cell raised NameError: name 'HookedTransformer' is not defined.

This completes the alignment for the LIT demo:

• Updates model loading from HookedTransformer.from_pretrained to TransformerBridge.boot_transformers("gpt2") with enable_compatibility_mode().
• Updates the following markdown cell to refer to model instead of HookedTransformer.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have not rewritten tests relating to key interfaces which would affect backward compatibility

[jlarson4]

Great work on this @ZacharyZcR! Thanks for tackling it!