Upgrade to webtorrent v2 (avoid downloads in RAM)

Main advantage of webtorrent v2: it [uses local storage](https://github.com/webtorrent/webtorrent/blob/v2.4.14/docs/api.md?plain=1#L120) as opposed to keeping the complete files in memory.

This is more scalable in terms of file size, and allows users to upload entire folders (with nested structure) to a receiver-specified local folder. Currently blaze is limited to a flat list of files going to the browser downloads.

Started the discussion here: https://github.com/blenderskool/blaze/pull/174#discussion_r1701773132

Potential implementation elaborated here: https://github.com/webtorrent/webtorrent/issues/2849

Start with the linked PR discussion and the WebTorrent issue to understand the proposed v2 integration and its local-storage behavior. The work is done when Blaze no longer keeps complete files in memory and supports uploading nested folders to a receiver-specified local folder instead of only browser downloads.

Written by the indexing model from the issue text.