feat: Adds VitEncoder for visual transformers

[bruvduroiu]

TODO:

• formalise Pydantic types for routes
• more unit tests that cover torch
• documentation

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (544a6ba) 83.82% compared to head (797544c) 84.30%.

Files	Patch %	Lines
semantic_router/encoders/vit.py	98.24%	1 Missing ⚠️
semantic_router/index/local.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
+ Coverage   83.82%   84.30%   +0.48%     
==========================================
  Files          35       36       +1     
  Lines        1632     1695      +63     
==========================================
+ Hits         1368     1429      +61     
- Misses        264      266       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.