Add arithmetic_chain community environment

Procedural multi-step integer chains with boxed answers; uses ManagedServer
and math_verify for scoring. No external dataset required.

Made-with: Cursor

environments/community/arithmetic_chain/README.md

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+# Arithmetic Chain
+
+Self-contained RL environment: procedurally generated multi-step integer problems (add / subtract / multiply from a starting value). The model must answer with `\boxed{integer}`; rewards use the same `math_verify` path as GSM8K.
+
+**No Hugging Face dataset** — training items are sampled on the fly.
+
+## Run (serve)
+
+From the repo root, with Atropos API and an OpenAI-compatible inference server configured in `config_init` or via CLI overrides:
+
+```bash
+python environments/community/arithmetic_chain/arithmetic_chain_server.py serve --slurm false
+```
+
+## Process (debug rollouts)
+
+```bash
+python environments/community/arithmetic_chain/arithmetic_chain_server.py process \
+  --env.data_path_to_save_groups rollouts.jsonl \
+  --slurm false
+```
+
+Uses `ManagedServer` for token/logprob tracking (compatible with trainers that expect Atropos’ standard scored groups).