Improve downloader

[Frando]

Currently the iroh::downloader module is only used for iroh sync. Regular downloads (for blob download) are using the iroh bytes API directly. What we want to do is:

• Move the downloader iroh-bytes
• Improve downloader and enable use in iroh node for blob downloads
  • feat(iroh-bytes)!: refactor downloader queue and add progress reporting #2085
  • feat: retry nodes in downloader #2165
• Improve content downloading in docs:
  • refactor: improve content downloading in docs #2127
• Support content discovery and announcements in the downloader

[dignifiedquire]

Most of the originally planned work here was done, closing this