Promote dev to main: add gpt-5.5 family and claude-opus-4-7

[yuxiang-wu]

Promotes the current dev to main. Single commit:

• Add gpt-5.5 family and claude-opus-4-7 to README model list (Add gpt-5.5 family and claude-opus-4-7 to README model list #144)
  • GPT-5: gpt-5.5, gpt-5.5-pro, gpt-5.4, gpt-5.4-pro, gpt-5.4-mini, gpt-5.3-codex
  • Anthropic: claude-opus-4-7
  • Drops the stale "(37 total)" count

Pairs with the proxy PR in litellm-gcp-cloud-run that exposes these models.

Test plan

• CLI hello-world example with --model gpt-5.5 and --model claude-opus-4-7 works against dev
• README renders correctly on PyPI / GitHub after publish