v1.4.568

Changes

PR #2338 by ksylvan: feat(anthropic): upgrade to anthropic-sdk-go v2.8.0

• Upgraded the Anthropic SDK to v2 while preserving Claude compatibility, including migrated Anthropic, Vertex AI, and error handling imports.
• Upgraded Go to 1.26.10 and refreshed project dependencies.
• Preserved legacy sampling controls across requests and beta retries, with Vertex AI sampling requests pinned to the legacy version.
• Restricted X-Api-Key authentication to custom Anthropic endpoints only.
• Added support for the Claude Fable 5.2 and Mythos 5.2 models.