fix: resolve cargo check errors and warnings

These were introduced by the change to edition 2024 and rust 1.86

Authored with support from Zed AI using Claude Sonnet 4.5

- find_subtree_roots has been dead code for 3.5 years!
  - see `git log -S find_subtree_roots`
  - see dd45eb8

Author: claytonrcarter

git-branchless-invoke/src/lib.rs

@@ -69,7 +69,11 @@ fn install_tracing(effects: Effects) -> eyre::Result<impl Drop> {
             Ok(nesting_level) => nesting_level.parse::<usize>().unwrap_or_default(),
             Err(_) => 0,
         };
-        std::env::set_var(NESTING_LEVEL_KEY, (nesting_level + 1).to_string());
+        // SAFETY: We're setting an environment variable that we control and read immediately
+        // after. This is done at the start of execution before any threading occurs.
+        unsafe {
+            std::env::set_var(NESTING_LEVEL_KEY, (nesting_level + 1).to_string());
+        }
 
         let should_include_function_args = match std::env::var("RUST_PROFILE_INCLUDE_ARGS") {
             Ok(value) if !value.is_empty() => true,

git-branchless-lib/src/git/repo.rs

@@ -1540,7 +1540,7 @@ impl Repo {
             let mut result = self.get_paths_touched_by_commit(parent_commit)?;
             match opts {
                 AmendFastOptions::FromIndex { paths } => result.extend(paths.iter().cloned()),
-                AmendFastOptions::FromWorkingCopy { ref status_entries } => {
+                AmendFastOptions::FromWorkingCopy { status_entries } => {
                     for entry in status_entries {
                         result.extend(entry.paths().iter().cloned());
                     }

git-branchless-reword/src/lib.rs

@@ -673,32 +673,6 @@ fn parse_bulk_edit_message(
     })
 }
 
-/// Return the root commits for given a list of commits. This is the list of commits that have *no*
-/// ancestors also in the list. The idea is to find the minimum number of subtrees that much be
-/// rebased to include all of our rewording.
-#[instrument]
-fn find_subtree_roots<'repo>(
-    repo: &'repo Repo,
-    dag: &Dag,
-    commits: &[Commit],
-) -> eyre::Result<Vec<Commit<'repo>>> {
-    let commits: CommitSet = commits.iter().map(|commit| commit.get_oid()).collect();
-
-    // Find the vertices representing the roots of this set of commits
-    let subtree_roots = dag
-        .query_roots(commits)
-        .wrap_err("Computing subtree roots")?;
-
-    // convert the vertices back into actual Commits
-    let root_commits = dag
-        .commit_set_to_vec(&subtree_roots)?
-        .into_iter()
-        .filter_map(|oid| repo.find_commit(oid).ok()?)
-        .collect();
-
-    Ok(root_commits)
-}
-
 /// Print a basic status report of what commits were reworded.
 #[instrument]
 fn render_status_report(