feat: use gix-negotiate in fetch machinery.

Thanks to it we are finally able to do pack negotiations just like git can,
as many rounds as it takes and with all available algorithms.

Author: Byron

gix/tests/fixtures/make_remote_repos.sh

@@ -308,3 +308,45 @@ git clone --shared base detached-head
 (cd detached-head
   git checkout @~1
 )
+
+function commit() {
+  local message=${1:?first argument is the commit message}
+  local file="$message.t"
+  echo "$1" > "$file"
+  git add -- "$file"
+  tick
+  git commit -m "$message"
+  git tag "$message"
+}
+
+function optimize_repo() {
+  git commit-graph write --no-progress --reachable
+  git repack -adq
+}
+
+(mkdir multi_round && cd multi_round
+  git init -q server && cd server
+    commit to_fetch
+  cd ..
+
+  git init -q client && cd client
+    for i in $(seq 8); do
+      git checkout --orphan b$i &&
+      commit b$i.c0
+    done
+
+    for j in $(seq 19); do
+      for i in $(seq 8); do
+        git checkout b$i &&
+        commit b$i.c$j
+      done
+    done
+    optimize_repo
+  cd ..
+  (cd server
+    git fetch --no-tags "$PWD/../client" b1:refs/heads/b1
+    git checkout b1
+    commit commit-on-b1
+    optimize_repo
+  )
+)

gix/tests/remote/fetch.rs

@@ -19,6 +19,7 @@ mod blocking_and_async_io {
     use gix_protocol::maybe_async;
 
     use crate::{
+        remote,
         remote::{into_daemon_remote_if_async, spawn_git_daemon_if_async},
         util::hex_to_id,
     };
@@ -106,6 +107,25 @@ mod blocking_and_async_io {
         Ok(())
     }
 
+    // TODO: try this as maybe-async
+    #[test]
+    #[cfg(feature = "blocking-network-client")]
+    #[ignore = "fails because of improper negotiation (it's hacked to work for our cases)"]
+    fn fetch_with_multi_round_negotiation() -> crate::Result {
+        let repo = remote::repo("multi_round/client");
+        let server_repo = remote::repo("multi_round/server");
+        let changes = repo
+            .remote_at(server_repo.work_dir().expect("non-bare"))?
+            .with_refspecs(Some("refs/heads/*:refs/remotes/origin/*"), Fetch)?
+            .connect(Fetch)?
+            .prepare_fetch(gix::progress::Discard, Default::default())?
+            .with_dry_run(true)
+            .receive(gix::progress::Discard, &AtomicBool::default())?;
+
+        dbg!(changes);
+        Ok(())
+    }
+
     #[maybe_async::test(
         feature = "blocking-network-client",
         async(feature = "async-network-client-async-std", async_std::test)