fix(telegram): dynamic rolling buffer video cache (Fixes #376)

[Himanth-reddy]

Summary of Changes

Fixes #376 by implementing a YouTube/Stremio-style Dynamic Rolling Window Buffer for Telegram video streaming with low-storage protection.

Features & Adjustments:

1. Dynamic Bitrate-Based Buffer Calculation:
   • Calculates average byte rate based on total file size.
   • Bounds prefetching to a 2.5 minute (150s) lookahead window (20 MB - 300 MB max) with a 30s rewind window.
2. Low-Storage Protection:
   • Drops prefetch size down to 2 MB if usable storage falls below 500 MB.
   • Invokes TdApi.OptimizeStorage if usable storage falls below 200 MB.
3. Immediate Cleanup:
   • Automatically deletes active stream files from disk when switching videos, stopping playback, or exiting the app.