Improve HTTP and Poster performance

[0SkillAllLuck]

Improve the performance of HTTP requests and poster rendering by doing the following:

• Request pre-sized posters from Plex instead of always rescaling locally.
• Use posterWithProgress only if there is progress
• Cache textures in memory to speedup the UI rendering
• Tune HTTP pools to reduce TLS handshake churn
• Change the cache format to be binary encoding to speedup cache layer
• Increase the memory cap for in memory cache to prevent cache exhaustion