Use a standard HashMap instead of one based on SHA1

It's faster throughout the board.

```
❯ cargo bench -p [email protected] --bench edit-tree
   Compiling gix-object v0.44.0 (/Users/byron/dev/github.com/Byron/gitoxide/gix-object)
   Compiling gix-pack v0.53.0 (/Users/byron/dev/github.com/Byron/gitoxide/gix-pack)
   Compiling gix-odb v0.63.0 (/Users/byron/dev/github.com/Byron/gitoxide/gix-odb)
    Finished `bench` profile [optimized] target(s) in 5.97s
     Running benches/edit_tree.rs (target/release/deps/edit_tree-6af6651a1c453a05)
Gnuplot not found, using plotters backend
editor/small tree (empty -> full -> empty)
                        time:   [2.5972 µs 2.6019 µs 2.6075 µs]
                        thrpt:  [3.8351 Melem/s 3.8434 Melem/s 3.8503 Melem/s]
                 change:
                        time:   [-32.618% -32.355% -32.038%] (p = 0.00 < 0.05)
                        thrpt:  [+47.142% +47.831% +48.409%]
                        Performance has improved.
Found 14 outliers among 100 measurements (14.00%)
  13 (13.00%) high mild
  1 (1.00%) high severe
editor/deeply nested tree (empty -> full -> empty)
                        time:   [8.2019 µs 8.2079 µs 8.2145 µs]
                        thrpt:  [5.5998 Melem/s 5.6043 Melem/s 5.6084 Melem/s]
                 change:
                        time:   [-33.517% -33.377% -33.246%] (p = 0.00 < 0.05)
                        thrpt:  [+49.804% +50.099% +50.415%]
                        Performance has improved.
Found 13 outliers among 100 measurements (13.00%)
  8 (8.00%) high mild
  5 (5.00%) high severe

cursor/small tree (empty -> full -> empty)
                        time:   [2.6911 µs 2.6935 µs 2.6961 µs]
                        thrpt:  [3.7090 Melem/s 3.7127 Melem/s 3.7160 Melem/s]
                 change:
                        time:   [-33.881% -33.546% -33.225%] (p = 0.00 < 0.05)
                        thrpt:  [+49.757% +50.480% +51.242%]
                        Performance has improved.
Found 14 outliers among 100 measurements (14.00%)
  4 (4.00%) high mild
  10 (10.00%) high severe
cursor/deeply nested tree (empty -> full -> empty)
                        time:   [1.3616 µs 1.3631 µs 1.3649 µs]
                        thrpt:  [33.703 Melem/s 33.747 Melem/s 33.783 Melem/s]
                 change:
                        time:   [-40.063% -39.675% -39.234%] (p = 0.00 < 0.05)
                        thrpt:  [+64.566% +65.769% +66.843%]
                        Performance has improved.
Found 20 outliers among 100 measurements (20.00%)
  18 (18.00%) high mild
  2 (2.00%) high severe
```

Author: Byron

gix-object/src/tree/editor.rs

@@ -2,8 +2,8 @@ use crate::tree::{Editor, EntryKind};
 use crate::{tree, Tree};
 use bstr::{BStr, BString, ByteSlice, ByteVec};
 use gix_hash::ObjectId;
-use gix_hashtable::hash_map::Entry;
 use std::cmp::Ordering;
+use std::collections::{hash_map, HashMap};
 
 /// A way to constrain all [tree-edits](Editor) to a given subtree.
 pub struct Cursor<'a, 'find> {
@@ -24,7 +24,7 @@ impl<'a> Editor<'a> {
         Editor {
             find,
             object_hash,
-            trees: gix_hashtable::HashMap::from_iter(Some((empty_path_hash(), root))),
+            trees: HashMap::from_iter(Some((empty_path(), root))),
             path_buf: Vec::with_capacity(256).into(),
             tree_buf: Vec::with_capacity(512),
         }
@@ -259,8 +259,8 @@ impl<'a> Editor<'a> {
             push_path_component(&mut self.path_buf, name);
             let path_id = path_hash(&self.path_buf);
             cursor = match self.trees.entry(path_id) {
-                Entry::Occupied(e) => e.into_mut(),
-                Entry::Vacant(e) => e.insert(
+                hash_map::Entry::Occupied(e) => e.into_mut(),
+                hash_map::Entry::Vacant(e) => e.insert(
                     if let Some(tree_id) = tree_to_lookup.filter(|tree_id| !tree_id.is_empty_tree()) {
                         self.find.find_tree(&tree_id, &mut self.tree_buf)?.into()
                     } else {
@@ -279,7 +279,7 @@ impl<'a> Editor<'a> {
     /// This is useful if the same editor is re-used for various trees.
     pub fn set_root(&mut self, root: Tree) -> &mut Self {
         self.trees.clear();
-        self.trees.insert(empty_path_hash(), root);
+        self.trees.insert(empty_path(), root);
         self
     }
 }
@@ -387,14 +387,12 @@ fn filename(path: &BStr) -> &BStr {
     path.rfind_byte(b'/').map_or(path, |pos| &path[pos + 1..])
 }
 
-fn empty_path_hash() -> ObjectId {
-    gix_features::hash::hasher(gix_hash::Kind::Sha1).digest().into()
+fn empty_path() -> BString {
+    BString::default()
 }
 
-fn path_hash(path: &[u8]) -> ObjectId {
-    let mut hasher = gix_features::hash::hasher(gix_hash::Kind::Sha1);
-    hasher.update(path);
-    hasher.digest().into()
+fn path_hash(path: &[u8]) -> BString {
+    path.to_vec().into()
 }
 
 fn push_path_component(base: &mut BString, component: &[u8]) -> usize {

gix-object/src/tree/mod.rs

@@ -2,7 +2,6 @@ use crate::{
     bstr::{BStr, BString},
     tree, Tree,
 };
-use gix_hash::ObjectId;
 use std::cmp::Ordering;
 
 ///
@@ -19,12 +18,6 @@ pub mod write;
 ///
 /// The editor is optimized to edit existing trees, but can deal with building entirely new trees as well
 /// with some penalties.
-///
-/// ### Note
-///
-/// For reasons of efficiency, internally a SHA1 based hashmap is used to avoid having to store full paths
-/// to each edited tree. The chance of collision is low, but could be engineered to overwrite or write into
-/// an unintended tree.
 #[doc(alias = "TreeUpdateBuilder", alias = "git2")]
 #[derive(Clone)]
 pub struct Editor<'a> {
@@ -35,7 +28,7 @@ pub struct Editor<'a> {
     /// All trees we currently hold in memory. Each of these may change while adding and removing entries.
     /// null-object-ids mark tree-entries whose value we don't know yet, they are placeholders that will be
     /// dropped when writing at the latest.
-    trees: gix_hashtable::HashMap<ObjectId, Tree>,
+    trees: std::collections::HashMap<BString, Tree>,
     /// A buffer to build up paths when finding the tree to edit.
     path_buf: BString,
     /// Our buffer for storing tree-data in, right before decoding it.