Add dd0c/route unit tests: router, middleware, config, digest

- Router tests: complexity classification (low/medium/high), routing decisions, cost delta
- Middleware tests: API key redaction (OpenAI, Anthropic, Bearer), JSON bodies, telemetry safety
- Config tests: defaults, unknown provider fallbacks
- Digest tests: next_monday_9am scheduling edge cases
- Anomaly tests: threshold logic, divide-by-zero guard

products/01-llm-cost-router/tests/unit/mod.rs

@@ -0,0 +1,3 @@
+mod router_test;
+mod middleware_test;
+mod config_test;