fix(call): improve virtual background performance

[Antreesy]

☑️ Resolves

Reduce GPU load while maintaining similar blur/mask quality and responsiveness

• After isolation tests, several items were marked as having an impact on GPU load, from low to high:
  • DEFAULT_BLUR_PASSES - Larger value - stronger blur effect. Low GPU impact.
  • SIGMA_SPACE - Larger value - smoother mask over a wider area, softer edges. High GPU impact.
  • MAX_SEGMENTATION_FRAME_RATE - Larger value - more often mask is segmented from video. High GPU impact.
  • SIGMA_COLOR - Larger value: more smoothing across edges. Low GPU impact.
  • SPARSITY_FACTOR - Larger value - faster processing, rougher mask refinement. High GPU impact.
• All values are configurable in source code, so we need to find appropriate resulting picture, that doesn't consume much memory

As refence - Zoom allows to login -> Meet -> Host a meeting -> Check your camera with virtual BG there.

AI (if applicable)

• The content of this PR was partly or fully generated using AI

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

Tested on Windows with Intel(R) UHD Graphincs

🏚️ Before	🏡 After	🔧 Tuned	Zoom

🚧 Tasks

• Find appropriate values that looks fine on different devices /cameras -> splitted
• Check for possible mask freezing in _runInference with active video frame and _postProcessing
• Uncaught (in promise) RuntimeError: divide by zero
• Other errors

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required