message: feat: Add a method to get mutable access of v1 field
diff: @@ -36,6 +36,10 @@ impl CrateListingV1 {
  pub fn v1(&self) -> &BTreeMap<PackageId, BTreeSet<String>> {
  &self.v1
  }
  +
  + pub fn v1_mut(&mut self) -> &mut BTreeMap<PackageId, BTreeSet<String>> {
  + &mut self.v1
  + }
  }
  pub fn resolve_root(flag: Option<&str>, config: &Config) -> CargoResult<Filesystem> {
  