feat: implement BEP-53 support

[PastaPastaPasta]

Implement support for BEP-53 Select Only magnet extension

This does not include full support in the GUI / web interface. When initially adding a torrent with SO, the gui will show ALL as selected, even though the actual download will only download the sections needed for that file. Once a torrent has been added, the file list then becomes accurate.

See below patch, for how I tried to have the UI be reactive to so= however, this patch didn't work. I'd love to get feedback on a patch that works, but even without I think this PR is valuable and net positive

diff --git a/crates/librqbit/webui/src/components/modal/FileSelectionModal.tsx b/crates/librqbit/webui/src/components/modal/FileSelectionModal.tsx
index 0a41f33..d767c60 100644
--- a/crates/librqbit/webui/src/components/modal/FileSelectionModal.tsx
+++ b/crates/librqbit/webui/src/components/modal/FileSelectionModal.tsx
@@ -1,5 +1,5 @@
 import { useContext, useEffect, useState } from "react";
-import { AddTorrentResponse, AddTorrentOptions } from "../../api-types";
+import {AddTorrentResponse, AddTorrentOptions, TorrentDetails} from "../../api-types";
 import { APIContext } from "../../context";
 import { ErrorComponent } from "../ErrorComponent";
 import { ErrorWithLabel } from "../../rqbit-web";
@@ -34,6 +34,8 @@ export const FileSelectionModal = (props: {
   const [uploadError, setUploadError] = useState<ErrorWithLabel | null>(null);
   const [unpopularTorrent, setUnpopularTorrent] = useState(false);
   const [outputFolder, setOutputFolder] = useState<string>("");
+  const [detailsResponse, updateDetailsResponse] =
+      useState<TorrentDetails | null>(null);
   const refreshTorrents = useTorrentStore((state) => state.refreshTorrents);
   const API = useContext(APIContext);
 
@@ -76,6 +78,18 @@ export const FileSelectionModal = (props: {
         () => {
           onHide();
           refreshTorrents();
+          useEffect(() => {
+            console.log('trying to set selected files');
+            setSelectedFiles(
+                new Set<number>(
+                    detailsResponse?.files
+                        .map((f, id) => ({ f, id }))
+                        .filter(({ f }) => f.included)
+                        .map(({ id }) => id) ?? []
+                )
+            );
+          }, [detailsResponse]);
+
         },
         (e) => {
           setUploadError({ text: "Error starting torrent", details: e });

[ikatson]

Thanks @PastaPastaPasta for the PR! Agree it makes sense even without UI support, so can merge this first. Added a few minor comments, should be very quick to address.

[ikatson]

@PastaPastaPasta if you want to fix the UI, I think an easy fix would be to:

1. in Rust, include only_files as part of AddTorrentResponse, including list_only. This would carry "so" and only_files logic all the way back through the API to JS
2. In JS FileSelectionModal, use that instead of this piece

setSelectedFiles(
    new Set(listTorrentResponse?.details.files.map((_, i) => i)),
);