Avoid recomputing fuzzy match scores (#13700)

<!--
if this PR closes one or more issues, you can automatically link the PR
with
them by using one of the [*linking
keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword),
e.g.
- this PR should close #xxxx
- fixes #xxxx

you can also mention related issues, PRs or discussions!
-->

# Description
<!--
Thank you for improving Nushell. Please, check our [contributing
guide](../CONTRIBUTING.md) and talk to the core team before making major
changes.

Description of your pull request goes here. **Provide examples and/or
screenshots** if your changes affect the user experience.
-->

This PR makes it so that when using fuzzy matching, the score isn't
recomputed when sorting. Instead, filtering and sorting suggestions is
handled by a new `NuMatcher` struct. This struct accepts suggestions
and, if they match the user's typed text, stores those suggestions
(along with their scores and values). At the end, it returns a sorted
list of suggestions.

This probably won't have a noticeable impact on performance, but it
might be helpful if we start using Nucleo in the future.

Minor change: Makes `find_commands_by_predicate` in `StateWorkingSet`
and `EngineState` take `FnMut` rather than `Fn` for the predicate.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

When using case-insensitive matching, if you have two matches `FOO` and
`abc`, `abc` will be shown before `FOO` rather than the other way
around. I think this way makes more sense than the current behavior.
When I brought this up on Discord, WindSoilder did say it would make
sense to show uppercase matches first if the user typed, say, `F`.
However, that would be a lot more complicated to implement.

# Tests + Formatting
<!--
Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

Added a test for the changes in
https://github.com/nushell/nushell/pull/13302.

# After Submitting
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
-->

crates/nu-cli/tests/completions/mod.rs

@@ -890,8 +890,8 @@ fn subcommand_completions(mut subcommand_completer: NuCompleter) {
     match_suggestions(
         &vec![
             "foo bar".to_string(),
-            "foo aabcrr".to_string(),
             "foo abaz".to_string(),
+            "foo aabcrr".to_string(),
         ],
         &suggestions,
     );
@@ -955,8 +955,8 @@ fn flag_completions() {
         "--mime-type".into(),
         "--short-names".into(),
         "--threads".into(),
-        "-D".into(),
         "-a".into(),
+        "-D".into(),
         "-d".into(),
         "-f".into(),
         "-h".into(),
@@ -1287,7 +1287,7 @@ fn variables_completions() {
     assert_eq!(3, suggestions.len());
 
     #[cfg(windows)]
-    let expected: Vec<String> = vec!["PWD".into(), "Path".into(), "TEST".into()];
+    let expected: Vec<String> = vec!["Path".into(), "PWD".into(), "TEST".into()];
     #[cfg(not(windows))]
     let expected: Vec<String> = vec!["PATH".into(), "PWD".into(), "TEST".into()];
 
@@ -1576,6 +1576,23 @@ fn sort_fuzzy_completions_in_alphabetical_order(mut fuzzy_alpha_sort_completer:
     );
 }
 
+#[test]
+fn exact_match() {
+    let (dir, _, engine, stack) = new_partial_engine();
+
+    let mut completer = NuCompleter::new(Arc::new(engine), Arc::new(stack));
+
+    let target_dir = format!("open {}", folder(dir.join("pArTiAL")));
+    let suggestions = completer.complete(&target_dir, target_dir.len());
+
+    // Since it's an exact match, only 'partial' should be suggested, not
+    // 'partial-a' and stuff. Implemented in #13302
+    match_suggestions(
+        &vec![file(dir.join("partial").join("hello.txt"))],
+        &suggestions,
+    );
+}
+
 #[ignore = "was reverted, still needs fixing"]
 #[rstest]
 fn alias_offset_bug_7648() {