fix: resolve bugs and improve code quality across the codebase

[coryrylan]

• Fix render data bug: use conf (with defaults) instead of raw config
  for returned iterations/average values in testRenderTime (browser.ts)
• Fix property name mismatch: server reads payload.average instead of
  payload.averages to match what the browser sends (index.ts)
• Add BundleConfig type annotation to bundlePerformancePlugin parameter
• Add explicit types to measureRenderTime session and payload parameters
• Fix shadowed path variable in performanceReporter (rename to reportPath)
  and use path.join for proper path construction
• Replace as any cast with type guard for CSS asset detection
• Add try/finally around rolldown pipeline to ensure bundle.close() runs
• Add timeout to measureElementRender to prevent hanging promises
• Add store reset after reporter writes to prevent data bleed across runs
• Fix LICENSE.md -> LICENSE in package.json files array
• Add tests for store accumulation, store reset, and RegExp alias patterns
• Add browser test for default testRenderTime config values
• Update test payloads to use correct property name (average vs averages)

https://claude.ai/code/session_01Qx5BGgWeYmPTnb8kwb56rg