Allocate less when doing a capture discovery (#8903)

# Description

This should be a little more efficient when running the algorithm to
find the captured variables.

# User-Facing Changes
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helps us keep track of breaking changes. -->

# Tests + Formatting
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- `cargo fmt --all -- --check` to check standard code formatting (`cargo
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src/tests.rs

@@ -48,6 +48,24 @@ pub fn run_test(input: &str, expected: &str) -> TestResult {
     let mut file = NamedTempFile::new()?;
     let name = file.path();
 
+    let mut cmd = Command::cargo_bin("nu")?;
+    cmd.arg("--no-std-lib");
+    cmd.arg(name);
+    cmd.env(
+        "PWD",
+        std::env::current_dir().expect("Can't get current dir"),
+    );
+
+    writeln!(file, "{input}")?;
+
+    run_cmd_and_assert(cmd, expected)
+}
+
+#[cfg(test)]
+pub fn run_test_std(input: &str, expected: &str) -> TestResult {
+    let mut file = NamedTempFile::new()?;
+    let name = file.path();
+
     let mut cmd = Command::cargo_bin("nu")?;
     cmd.arg(name);
     cmd.env(
@@ -83,6 +101,7 @@ pub fn run_test_contains(input: &str, expected: &str) -> TestResult {
     let name = file.path();
 
     let mut cmd = Command::cargo_bin("nu")?;
+    cmd.arg("--no-std-lib");
     cmd.arg(name);
 
     writeln!(file, "{input}")?;
@@ -108,6 +127,7 @@ pub fn test_ide_contains(input: &str, ide_commands: &[&str], expected: &str) ->
     let name = file.path();
 
     let mut cmd = Command::cargo_bin("nu")?;
+    cmd.arg("--no-std-lib");
     for ide_command in ide_commands {
         cmd.arg(ide_command);
     }
@@ -136,6 +156,7 @@ pub fn fail_test(input: &str, expected: &str) -> TestResult {
     let name = file.path();
 
     let mut cmd = Command::cargo_bin("nu")?;
+    cmd.arg("--no-std-lib");
     cmd.arg(name);
     cmd.env(
         "PWD",

src/tests/test_stdlib.rs

@@ -1,8 +1,8 @@
-use crate::tests::{fail_test, run_test, TestResult};
+use crate::tests::{fail_test, run_test_std, TestResult};
 
 #[test]
 fn library_loaded() -> TestResult {
-    run_test(
+    run_test_std(
         "help std | lines | first 1 | to text",
         "std.nu, `used` to load all standard library components",
     )
@@ -10,7 +10,7 @@ fn library_loaded() -> TestResult {
 
 #[test]
 fn prelude_loaded() -> TestResult {
-    run_test("std help commands | where name == open | length", "1")
+    run_test_std("std help commands | where name == open | length", "1")
 }
 
 #[test]
@@ -20,5 +20,5 @@ fn not_loaded() -> TestResult {
 
 #[test]
 fn use_command() -> TestResult {
-    run_test("use std assert; assert true; print 'it works'", "it works")
+    run_test_std("use std assert; assert true; print 'it works'", "it works")
 }