### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

When using LiteLLM's `/v1/chat/completions` endpoint with Anthropic models, multi-turn conversations involving tool calls break in several ways when the client sends messages in Anthropic content block format (i.e. `tool_use` in assistant `content` list, `tool_result` in user `content` list) rather than OpenAI `tool_calls` array format:

1. `_is_orphaned_tool_result()` in `sanitize_messages_for_tool_calling()` only checks `tool_calls` array for matching tool IDs. It never checks `content[type=tool_use]` blocks. Result: every `tool_result` message is flagged as orphaned and stripped, destroying conversation history. The model never sees tool results and re-runs the same tools indefinitely in a loop.

2. `anthropic_messages_pt()` processes assistant messages with a content list but has no handler for `type=tool_use` blocks. They are silently dropped. Same loop effect.

3. `anthropic_messages_pt()` processes user messages with a content list but has no handler for `type=tool_result` blocks. They are silently dropped. Anthropic then errors: `tool_u…