replace std hashmap with hashbrown hashmap

Cargo.toml

@@ -15,6 +15,7 @@ exclude = [".github/**", ".gitignore", ".rustfmt.toml"]
 
 [dependencies]
 typed-generational-arena = "0.2"
+hashbrown = "0.12.3"
 
 [dev-dependencies]
 lazy_static = "1.4.0"

src/index.rs

@@ -5,7 +5,7 @@ use std::{
 
 };
 
-use std::collections::{HashMap, HashSet};
+use hashbrown::{HashMap, HashSet};
 use crate::{FieldAccessor, Tokenizer};
 extern crate typed_generational_arena;
 use typed_generational_arena::StandardArena;

src/query.rs

@@ -2,7 +2,7 @@ use std::{
     fmt::Debug,
     hash::Hash,
 };
-use std::collections::{HashMap, HashSet};
+use hashbrown::{HashMap, HashSet};
 
 use typed_generational_arena::StandardArena;
 

src/score/calculator.rs

@@ -4,7 +4,7 @@ use crate::{
 };
 use std::{ fmt::Debug};
 use typed_generational_arena::StandardIndex as ArenaIndex;
-use std::collections::HashMap;
+use hashbrown::HashMap;
 
 pub struct TermData<'a> {
     // Current query term index.

src/score/default/bm25.rs

@@ -3,7 +3,7 @@
 */
 
 use std::{fmt::Debug};
-use std::collections::{HashMap};
+use hashbrown::{HashMap};
 
 use crate::{
     index::{DocumentDetails, DocumentPointer, InvertedIndexNode},