Enables Anthropic/Bedrock prompt caching for Claude routes via LiteLLM
cache_control_injection_points: system prompt + latest message everywhere,
plus tool_config on Bedrock Converse only (the sole route whose transform
consumes it; elsewhere it leaks as an unknown top-level field that native
Anthropic 400-rejects). Unmapped Bedrock Claude models run uncached instead
of crashing. Adds STRIX_PROMPT_CACHE opt-out (default on).