fix(edge): fix shared result tables in llm_limiter and incomplete reset in circuit_breaker

[levleontiev]

Summary

This PR fixes two significant bugs and adds performance optimizations in fairvisor/edge:

1. llm_limiter.lua: Shared Result Tables (Bug Fix)

   • Issue: The module used module-level tables _result and _reconcile_result to return results from check and reconcile. This caused data corruption when multiple rules/policies used the LLM limiter in the same request, or across concurrent requests in the same worker.
   • Fix: Removed shared tables and _clear_result. Updated functions to return new table literals.

2. circuit_breaker.lua: Incomplete Auto-Reset (Bug Fix)

   • Issue: The check functions auto-reset logic only deleted the state_key, but did not clear the rate_keys`. Since the sliding window calculation continued immediately after reset, it would see the old (high) rates and immediately re-trip the breaker.
   • Fix: Updated check to call _M.reset() which correctly clears both state and rate keys.

3. llm_limiter.lua: _simple_word_estimate Optimization (Perf)

   • Optimization: Replaced string.sub truncation with index-based scanning to avoid large memory allocations for large request bodies. Also replaced string.sub with string.byte in the backslash-scanning loop (Zero-Allocation policy).

4. saas_client.lua: Authorization Header Caching (Perf)

   • Optimization: Cached the rendered Bearer ... token in _state to avoid redundant string concatenations and validation regex on every SaaS API call (heartbeats, event flushes, config polls).

Testing

• Verified with multiple reproduction scripts (shared table corruption, CB reset, regex anchoring behavior).
• Ran all 649 unit tests via busted: All passed.