Add Criterion benchmarks for parser (#7686)

This PR sets up [Criterion](https://github.com/bheisler/criterion.rs)
for benchmarking in the main `nu` crate, and adds some simple parser
benchmarks.

To run the benchmarks, just do `cargo bench` or `cargo bench -- <regex
matching benchmark names>` in the repo root:

```bash
〉cargo bench -- parse
...
     Running benches/parser_benchmark.rs (target/release/deps/parser_benchmark-75d224bac82d5b0b)
parse_default_env_file  time:   [221.17 µs 222.34 µs 223.61 µs]
Found 8 outliers among 100 measurements (8.00%)
  5 (5.00%) high mild
  3 (3.00%) high severe

parse_default_config_file
                        time:   [1.4935 ms 1.4993 ms 1.5059 ms]
Found 11 outliers among 100 measurements (11.00%)
  7 (7.00%) high mild
  4 (4.00%) high severe
```

Existing benchmarks from `nu-plugin` have been moved into the main `nu`
crate to keep all our benchmarks in one place.

benches/parser_benchmark.rs

@@ -0,0 +1,34 @@
+use criterion::{criterion_group, criterion_main, BatchSize, Criterion};
+use nu_parser::parse;
+use nu_protocol::{Span, Value};
+use nu_utils::{get_default_config, get_default_env};
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let mut engine_state = nu_command::create_default_context();
+    // parsing config.nu breaks without PWD set
+    engine_state.add_env_var(
+        "PWD".into(),
+        Value::string("/some/dir".to_string(), Span::test_data()),
+    );
+
+    let default_env = get_default_env().as_bytes();
+    c.bench_function("parse_default_env_file", |b| {
+        b.iter_batched(
+            || nu_protocol::engine::StateWorkingSet::new(&engine_state),
+            |mut working_set| parse(&mut working_set, None, default_env, false, &[]),
+            BatchSize::SmallInput,
+        )
+    });
+
+    let default_config = get_default_config().as_bytes();
+    c.bench_function("parse_default_config_file", |b| {
+        b.iter_batched(
+            || nu_protocol::engine::StateWorkingSet::new(&engine_state),
+            |mut working_set| parse(&mut working_set, None, default_config, false, &[]),
+            BatchSize::SmallInput,
+        )
+    });
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);