Replace Anthropic library (anthropic-rs -> anthropic) and switch default recommended model (claude-3-5-sonnet-20240620 -> claude-3-7-sonnet-20250219)

Fixes https://github.com/etkecc/baibot/issues/22

Ultimate related to `anthropic-rs` hardcoding models as enumeration variants in the code
and not updating them. See:
- https://github.com/roushou/mesh/issues/1
- https://github.com/roushou/mesh/pull/2

https://github.com/cortesi/misanthropy was also considered as an
alternative, but it did not allow configuring the base API URL like our
old Anthropic library (`anthropic-rs`) and like our new choice (`anthropic`).
We'd rather not lose support for this, so we're going with the `anthropic` library.

docs/sample-provider-configs/anthropic.yml

@@ -1,7 +1,7 @@
 base_url: https://api.anthropic.com/v1
 api_key: YOUR_API_KEY_HERE
 text_generation:
-  model_id: claude-3-5-sonnet-20240620
+  model_id: claude-3-7-sonnet-20250219
   prompt: "You are a brief, but helpful bot called {{ baibot_name }} powered by the {{ baibot_model_id }} model. The date/time of this conversation's start is: {{ baibot_conversation_start_time_utc }}."
   temperature: 1.0
   max_response_tokens: 8192