Feature/llm multi prompt

[jubeless]

This PR introduces support for multi-prompt calls in llms, while maintaining backward compatibility with the LLMChain implementation for the call function. That said we believe the default of LLMChain.Call behaviour should not flatten prompts into a single message.

Key Features

• Add GenerateFromMultiPrompt support in llms.
• Ensure backward compatibility for chains.Calls when using GenerateFromMultiPrompt.

Backward Compatibility

No breaking changes have been introduced. Tracing is optional and does not affect existing functionality when disabled.

PR Checklist

• Read the Contributing documentation.
• Read the Code of conduct documentation.
• Name your Pull Request title clearly, concisely, and prefixed with the name of the primarily affected package you changed according to Good commit messages (such as memory: add interfaces for X, Y or util: add whizzbang helpers).
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. Fixes #123).
• Describes the source of new concepts.
• References existing implementations as appropriate.
• Contains test coverage for new functions.
• Passes all golangci-lint checks.