LiteLLM 1.15.13 fixes provider preservation and Anthropic cache token underreporting

LiteLLM version 1.15.13 addresses several bugs, including the preservation of provider on LiteLLM-routed models and the underreporting of Anthropic cache token usage.

• Hardens brittle LLM event-bus mocks.
• Bumps h2 to version 4.4.1 to address security vulnerability GHSA-6hr6-w5qg-qmwg.
• Adds a DOCS_TRANSLATIONS workflow for locale synchronization and fixes broken README links.