Pydantic AI v2.52.0 fixes web_fetch denial-of-service vulnerability and adds Claude Sonnet 5.5 support

Pydantic AI v2.52.0 fixes a medium-severity vulnerability (GHSA-v36g-jcw9-x7cw) in the local web_fetch tool: processing attacker-controlled deeply nested HTML consumes excessive CPU and memory. Provider-native fetching is not affected. The fix is in 2.52.0 (v2) and 1.107.7 (v1). This release also adds Claude Sonnet 5.5 and OpenAI gpt-6.1-sol support, and raises the default max_tokens for AnthropicModel from 4096 to 16384 on Claude Sonnet 4.5 and later.