Memory and goroutine leaks in long-running embedded engine usage

## Summary The embedded engine can leak memory and goroutines over time during long-running usage. ## Required changes Implement the leak-prevention work described in #7502: - bound the `HTTPToHTTPS` tracker with an LRU - release the per-host rate-limit pool goroutines on close - purge the template caches on engine close ## Rationale Without explicit cleanup and bounded caching, long-running embedders can accumulate memory usage and leave background goroutines running indefinitely. ## Affected areas - `HTTPToHTTPS` tracking / redirect bookkeeping - per-host rate limit pool lifecycle and shutdown - template cache lifecycle during engine close ## Acceptance criteria - The `HTTPToHTTPS` tracker is size-bounded and evicts old entries. - Per-host rate-limit pool goroutines are released when the engine closes. - Template caches are purged on engine close. - Long-running embedded usage no longer shows continued growth from these resources. ## Backlinks - Pull request: https://github.com/projectdiscovery/nuclei/pull/7502 - Request comment: https://github.com/projectdiscovery/nuclei/pull/7502#issuecomment-4794470056 - Requested by: @Mzack9999 ## Additional context PR title: fix leaks