Benchmark changes (#11998)

<!--
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 does a total of 3 things,
1. It fixes an error when running the `cargo bench` suit where nushell
constants where not set correctly ending in an error when running the
code.
2. It removes 2 redundant benchmark runs as these where duplicates of
existing ones.
3. It reduced encoding and decoding benchmark suit future, only having 4
benches instead of the previous 8.

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

# 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 std testing; testing run-tests --path
crates/nu-std"` 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
> ```
-->

# 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.
-->

benches/benchmarks.rs

@@ -2,7 +2,9 @@ use criterion::{criterion_group, criterion_main, BatchSize, Criterion};
 use nu_cli::eval_source;
 use nu_parser::parse;
 use nu_plugin::{Encoder, EncodingType, PluginCallResponse, PluginOutput};
-use nu_protocol::{engine::EngineState, PipelineData, Span, Value};
+use nu_protocol::{
+    engine::EngineState, eval_const::create_nu_constant, PipelineData, Span, Value, NU_VARIABLE_ID,
+};
 use nu_utils::{get_default_config, get_default_env};
 use std::path::{Path, PathBuf};
 
@@ -61,34 +63,6 @@ fn parser_benchmarks(c: &mut Criterion) {
             BatchSize::SmallInput,
         )
     });
-
-    c.bench_function("eval default_env.nu", |b| {
-        b.iter(|| {
-            let mut stack = nu_protocol::engine::Stack::new();
-            eval_source(
-                &mut engine_state,
-                &mut stack,
-                get_default_env().as_bytes(),
-                "default_env.nu",
-                PipelineData::empty(),
-                false,
-            )
-        })
-    });
-
-    c.bench_function("eval default_config.nu", |b| {
-        b.iter(|| {
-            let mut stack = nu_protocol::engine::Stack::new();
-            eval_source(
-                &mut engine_state,
-                &mut stack,
-                get_default_config().as_bytes(),
-                "default_config.nu",
-                PipelineData::empty(),
-                false,
-            )
-        })
-    });
 }
 
 fn eval_benchmarks(c: &mut Criterion) {
@@ -101,6 +75,10 @@ fn eval_benchmarks(c: &mut Criterion) {
         Value::string(home_path.to_string_lossy(), Span::test_data()),
     );
 
+    let nu_const = create_nu_constant(&engine_state, Span::unknown())
+        .expect("Failed to create nushell constant.");
+    engine_state.set_variable_const_val(NU_VARIABLE_ID, nu_const);
+
     c.bench_function("eval default_env.nu", |b| {
         b.iter(|| {
             let mut stack = nu_protocol::engine::Stack::new();
@@ -143,7 +121,7 @@ fn encoding_test_data(row_cnt: usize, col_cnt: usize) -> Value {
 
 fn encoding_benchmarks(c: &mut Criterion) {
     let mut group = c.benchmark_group("Encoding");
-    let test_cnt_pairs = [(100, 5), (100, 15), (10000, 5), (10000, 15)];
+    let test_cnt_pairs = [(100, 5), (10000, 15)];
     for (row_cnt, col_cnt) in test_cnt_pairs.into_iter() {
         for fmt in ["json", "msgpack"] {
             group.bench_function(&format!("{fmt} encode {row_cnt} * {col_cnt}"), |b| {
@@ -162,7 +140,7 @@ fn encoding_benchmarks(c: &mut Criterion) {
 
 fn decoding_benchmarks(c: &mut Criterion) {
     let mut group = c.benchmark_group("Decoding");
-    let test_cnt_pairs = [(100, 5), (100, 15), (10000, 5), (10000, 15)];
+    let test_cnt_pairs = [(100, 5), (10000, 15)];
     for (row_cnt, col_cnt) in test_cnt_pairs.into_iter() {
         for fmt in ["json", "msgpack"] {
             group.bench_function(&format!("{fmt} decode for {row_cnt} * {col_cnt}"), |b| {