v4.15.1

What's Changed

• feat(api): update API spec from langfuse/langfuse 74ded7e by @langfuse-bot in #1844
• perf(span-processor): skip span_formatter when debug logging is off by @DavidTraina in #1845
• refactor(logging): use lazy %-style formatting in log calls by @DavidTraina in #1846

Full Changelog: v4.15.0...v4.15.1