Add arsenal: 20 zero-dep Python libs for LLM agent failure modes

[darshjme]

arsenal (https://github.com/darshjme/arsenal) is a collection of 20 production-focused Python libraries that address the most common LLM agent failure modes.

What it covers:

• Routing and load balancing
• Budget management
• Input/output guardrails
• Memory compression
• Observability and tracing
• Retry/fallback logic
• Circuit breaking
• State management
• Schema validation
• Pipeline orchestration
• Semantic caching
• Config/secrets management
• Event bus
• Health checks
• Rate limiting

Why it belongs here:

• 808 tests — production-grade, not toy code
• Zero external dependencies — pure Python stdlib
• Each library is standalone and composable
• Directly addresses LLMOps pain points in production agent systems

Added to the LLMOps section.