Add A3M Router — code-focused LLM routing

[Das-rebel]

A3M Router — LLM routing for code tasks

• Missing reference #1 on RouterArena (76.43), cheapest at $0.047/1K
• Query-type presets including 'code' mode (temperature 0.3)
• Routes code queries to cheapest capable model
• 47+ providers (DeepSeek Coder, GPT-4, Claude, etc.)

GitHub: https://github.com/Das-rebel/a3m-router

[Das-rebel]

Hi! Just checking in on this PR. A3M Router is now #1 on RouterArena for robustness and has 20K+ npm downloads. Happy to update the description if needed. Thanks for considering!

[Das-rebel]

Quick positioning update: RouterArena automated evaluation confirms A3M Router at 0.9404 score / 96.77% accuracy, $0.0768/1K queries, and 1.0000 robustness with 0 abnormal entries across 8,400 queries. This positions A3M as No. 1 in accuracy, No. 1 in cost, and No. 1 in robustness among known public baselines: about 2.3× cheaper than Sqwish, 3.5× cheaper than RouteLLM, and ~130× cheaper than GPT-5.