Deprecate group in favor of chunks (#13377)

# Description
The name of the `group` command is a little unclear/ambiguous.
Everything I look at it, I think of `group-by`. I think `chunks` more
clearly conveys what the `group` command does. Namely, it divides the
input list into chunks of a certain size. For example,
[`slice::chunks`](https://doc.rust-lang.org/std/primitive.slice.html#method.chunks)
has the same name. So, this PR adds a new `chunks` command to replace
the now deprecated `group` command.

The `chunks` command is a refactored version of `group`. As such, there
is a small performance improvement:
```nushell
# $data is a very large list
> bench { $data | chunks 2 } --rounds 30 | get mean
474ms 921µs 190ns

# deprecation warning was disabled here for fairness
> bench { $data | group 2 } --rounds 30 | get mean
592ms 702µs 440ns



> bench { $data | chunks 200 } --rounds 30 | get mean
374ms 188µs 318ns

> bench { $data | group 200 } --rounds 30 | get mean
481ms 264µs 869ns 



> bench { $data | chunks 1 } --rounds 30 | get mean
642ms 574µs 42ns

> bench { $data | group 1 } --rounds 30 | get mean
981ms 602µs 513ns
```

# User-Facing Changes
- `group` command has been deprecated in favor of new `chunks` command.
- `chunks` errors when given a chunk size of `0` whereas `group` returns
chunks with one element.

# Tests + Formatting
Added tests for `chunks`, since `group` did not have any tests.

# After Submitting
Update book if necessary.

crates/nu-command/tests/commands/chunks.rs

@@ -0,0 +1,43 @@
+use nu_test_support::nu;
+
+#[test]
+fn chunk_size_negative() {
+    let actual = nu!("[0 1 2] | chunks -1");
+    assert!(actual.err.contains("positive"));
+}
+
+#[test]
+fn chunk_size_zero() {
+    let actual = nu!("[0 1 2] | chunks 0");
+    assert!(actual.err.contains("zero"));
+}
+
+#[test]
+fn chunk_size_not_int() {
+    let actual = nu!("[0 1 2] | chunks (if true { 1sec })");
+    assert!(actual.err.contains("can't convert"));
+}
+
+#[test]
+fn empty() {
+    let actual = nu!("[] | chunks 2 | is-empty");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn list_stream() {
+    let actual = nu!("([0 1 2] | every 1 | chunks 2) == ([0 1 2] | chunks 2)");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn table_stream() {
+    let actual = nu!("([[foo bar]; [0 1] [2 3] [4 5]] | every 1 | chunks 2) == ([[foo bar]; [0 1] [2 3] [4 5]] | chunks 2)");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn no_empty_chunks() {
+    let actual = nu!("([0 1 2 3 4 5] | chunks 3 | length) == 2");
+    assert_eq!(actual.out, "true");
+}

crates/nu-command/tests/commands/mod.rs

@@ -7,6 +7,7 @@ mod break_;
 mod bytes;
 mod cal;
 mod cd;
+mod chunks;
 mod compact;
 mod complete;
 mod config_env_default;