Add Phase 2 optimizations: status API caching and improved Redis pipelining

- Add in-memory cache for /status endpoint with 30s TTL
- Cache keyed by view parameters to handle different query patterns
- Add cache clearing for tests to prevent interference
- Optimize get_queue_metrics to use single pipeline for all Redis calls
  - Previously made 7+ separate pipeline calls
  - Now combines all queue metrics into one pipeline (7n+2 operations)
  - Reduces Redis round trips and improves API response time
- Update unit tests to match new pipelining behavior
- All 866 tests passing

spec/integration/api/v3/status_spec.rb

@@ -17,6 +17,8 @@ describe Vmpooler::API::V3 do
   # https://rubydoc.info/gems/sinatra/Sinatra/Base#reset!-class_method 
   before(:each) do
     app.reset!
+    # Clear status cache to prevent test interference
+    Vmpooler::API::V3.clear_status_cache
   end
 
   describe 'status and metrics endpoints' do