Add Claude Sonnet, Gemini 2.5 Pro models with special prices >200k tokens

[niharm]

There are a couple of major models that have special prices above 200k:

• Claude Sonnet 4
• Claude Sonnet 4.5
• Gemini 2.5 Pro

There are a couple of approaches here:

1. The approach taken by, e.g., llm-prices.com, which is to make the 200k models their own row

2. The approach taken by, e.g., LiteLLM, which is to add columns for the special prices

3. A more comprehensive solution, in which models can have special pricing columns that don't apply to all columns (say, a hash of special_prices).

In this PR, I implemented option 1 since I thought it was the least disruptive. LMK thoughts!

Gemini 2.5 Pro:
  - Input: $1.25 → $2.50
  - Output: $10.00 → $15.00
  - Cache read: $0.31 → $0.625

  Sonnet 4:
  - Input: $3.00 → $6.00
  - Output: $15.00 → $22.50
  - Cache read: $0.30 → $0.60
  - Cache write: $3.75 → $7.50

  Sonnet 4.5:
  - Input: $3.00 → $6.00
  - Output: $15.00 → $22.50
  - Cache read: $0.30 → $0.60
  - Cache write: $3.75 → $7.50

[fwang]

appreciate looking into the options! i'm leaning towards 2 or 3.. lemme give it some thought