Chore: clean up LLM (prompt caching, supports fn calling), leftover renames

[enyst]

Give a summary of what the PR does, explaining any non-trivial design decisions

This PR does a few clean-ups/leftovers

• Anthropic prompt caching is no longer in beta, so the header is not needed
• max cache markers is 4, remove potential 5th
• compute whether native function calling is enabled only once per LLM instance
• refactor out Cloudflare exception from llm.py

Also

• remove leak from runtime
• some leftover renaming eventstream->docker (for the runtime)

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Link of any specific issues this addresses
Fix #4484
Fix #6085

To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:5b795d1-nikolaik   --name openhands-app-5b795d1   docker.all-hands.dev/all-hands-ai/openhands:5b795d1