What does this PR do?

Adds prompt tracking support for LLM spans in LLMObs via a new WithAnnotatedPrompt annotation option.

Example usage:

ctx := context.Background()

span, ctx := llmobs.StartLLMSpan(ctx, "my-llm-call")
defer span.Finish()

input := []llmobs.LLMMessage{
    {Role: "system", Content: "You are a helpful assistant."},
    {Role: "user", Content: "{{question}}"},
}
output := []llmobs.LLMMessage{
    {Role: "assistant", Content: "The answer is 42."},
}

span.AnnotateLLMIO(input, output,
    llmobs.WithAnnotatedPrompt(llmobs.Prompt{
        ID:      "qa-prompt",
        Version: "1.0.0",
        Label:   "production",
        ChatTemplate: []llmobs.LLMMessage{
            {Role: "system", Content: "You are a helpful assistant."},
            {Role: "user", Content: "{{question}}"},
        },
        Variables: map[string]string{
            "question": "What is the answer to life?",
        },
        RAGQueryVariables: []string{"question"},
    }),
)

Additional changes:

• Adds WithAnnotatedToolDefinitions(toolDefinitions []ToolDefinition) annotation option for LLM spans.
• Renames WithIntent → WithAnnotatedIntent (old function deprecated, kept as alias)

Motivation

Prompt tracking LLMObs feature

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• New code is free of linting errors. You can check this by running make lint locally.
• New code doesn't break existing tests. You can check this by running make test locally.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• All generated files are up to date. You can check this by running make generate locally.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild. Make sure all nested modules are up to date by running make fix-modules locally.

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