fix(litellm): Set operation name from call type instead of chat fallback

[VihaanAgarwal]

Fixes #6442.

The input callback mapped every call type except embedding/aembedding to chat, so a litellm.image_generation() call showed up in Sentry as chat dall-e-3 with gen_ai.operation.name: chat. Same story for text completions, speech, transcription, rerank and the rest.

This replaces the binary fallback with an explicit table of the call types we can name accurately:

• completion/acompletion -> chat
• text_completion/atext_completion -> text_completion
• embedding/aembedding -> embeddings
• responses/aresponses -> responses

Each maps to its matching OP.GEN_AI_* span op (the constants for text_completion and responses already exist and are used by the langchain and openai integrations).

For everything else, gen_ai.operation.name is simply not set. Recording a guess is what this issue is about, and litellm has 140+ call types (batch, files, assistants, video...), most of which have no semconv equivalent. The raw call type still ends up in the span name (image_generation dall-e-3), so the spans stay identifiable. I kept gen_ai.chat as the span op fallback for unmapped types so those spans keep flowing into the AI views like before; happy to change that if you'd rather they drop out.

One test tweak: test_response_without_usage built callback kwargs without a call_type and asserted the span was named chat ..., which only held because of the fallback. Real callbacks always carry call_type (litellm's Logging.pre_call sets it), so I added "call_type": "completion" to those kwargs rather than special casing a missing key as chat.

Tests cover all eight mapped call types plus the unknown case. The litellm test module passes locally except test_multiple_providers, which errors at setup on current master too (missing optional provider package in my env).