Make the math commands const (#13566)

This PR closes [Issue
#13482](https://github.com/nushell/nushell/issues/13482)

# Description
This PR tend to make all math function to be constant. 

# User-Facing Changes
The math commands now can be used as constant methods.

### Some Example
```
> const MODE = [3 3 9 12 12 15] | math mode
> $MODE
╭───┬────╮
│ 0 │  3 │
│ 1 │ 12 │
╰───┴────╯

> const LOG = [16 8 4] | math log 2
> $LOG
╭───┬──────╮
│ 0 │ 4.00 │
│ 1 │ 3.00 │
│ 2 │ 2.00 │
╰───┴──────╯

> const VAR = [1 3 5] | math variance
> $VAR
2.6666666666666665
```

# Tests + Formatting
Tests are added for all of the math command to test there constant
behavior.

I mostly focused on the actual user experience, not the correctness of
the methods and algorithms.

# After Submitting
I think this change don't require any additional documentation. Feel
free to correct me in this topic please.

crates/nu-command/tests/commands/math/abs.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_abs() {
+    let actual = nu!("const ABS = -5.5 | math abs; $ABS");
+    assert_eq!(actual.out, "5.5");
+}

crates/nu-command/tests/commands/math/avg.rs

@@ -20,3 +20,9 @@ fn can_average_bytes() {
 
     assert_eq!(actual.out, "34985870");
 }
+
+#[test]
+fn const_avg() {
+    let actual = nu!("const AVG = [1 3 5] | math avg; $AVG");
+    assert_eq!(actual.out, "3");
+}

crates/nu-command/tests/commands/math/ceil.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_ceil() {
+    let actual = nu!("const CEIL = 1.5 | math ceil; $CEIL");
+    assert_eq!(actual.out, "2");
+}

crates/nu-command/tests/commands/math/floor.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_floor() {
+    let actual = nu!("const FLOOR = 15.5 | math floor; $FLOOR");
+    assert_eq!(actual.out, "15");
+}

crates/nu-command/tests/commands/math/log.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_log() {
+    let actual = nu!("const LOG = 16 | math log 2; $LOG");
+    assert_eq!(actual.out, "4");
+}

crates/nu-command/tests/commands/math/max.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_max() {
+    let actual = nu!("const MAX = [1 3 5] | math max; $MAX");
+    assert_eq!(actual.out, "5");
+}

crates/nu-command/tests/commands/math/median.rs

@@ -35,3 +35,9 @@ fn median_mixed_numbers() {
 
     assert_eq!(actual.out, "-11.5")
 }
+
+#[test]
+fn const_median() {
+    let actual = nu!("const MEDIAN = [1 3 5] | math median; $MEDIAN");
+    assert_eq!(actual.out, "3");
+}

crates/nu-command/tests/commands/math/min.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_min() {
+    let actual = nu!("const MIN = [1 3 5] | math min; $MIN");
+    assert_eq!(actual.out, "1");
+}

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

@@ -1,8 +1,18 @@
+mod abs;
 mod avg;
+mod ceil;
+mod floor;
+mod log;
+mod max;
 mod median;
+mod min;
+mod mode;
+mod product;
 mod round;
 mod sqrt;
+mod stddev;
 mod sum;
+mod variance;
 
 use nu_test_support::{nu, pipeline};
 

crates/nu-command/tests/commands/math/mode.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_avg() {
+    let actual = nu!("const MODE = [1 3 3 5] | math mode; $MODE");
+    assert_eq!(actual.out, "╭───┬───╮│ 0 │ 3 │╰───┴───╯");
+}

crates/nu-command/tests/commands/math/product.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_product() {
+    let actual = nu!("const PROD = [1 3 5] | math product; $PROD");
+    assert_eq!(actual.out, "15");
+}

crates/nu-command/tests/commands/math/round.rs

@@ -34,3 +34,9 @@ fn fails_with_wrong_input_type() {
 
     assert!(actual.err.contains("command doesn't support"))
 }
+
+#[test]
+fn const_round() {
+    let actual = nu!("const ROUND = 18.345 | math round; $ROUND");
+    assert_eq!(actual.out, "18");
+}

crates/nu-command/tests/commands/math/sqrt.rs

@@ -20,3 +20,9 @@ fn can_sqrt_perfect_square() {
 
     assert_eq!(actual.out, "2");
 }
+
+#[test]
+fn const_sqrt() {
+    let actual = nu!("const SQRT = 4 | math sqrt; $SQRT");
+    assert_eq!(actual.out, "2");
+}

crates/nu-command/tests/commands/math/stddev.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_avg() {
+    let actual = nu!("const SDEV = [1 2] | math stddev; $SDEV");
+    assert_eq!(actual.out, "0.5");
+}

crates/nu-command/tests/commands/math/sum.rs

@@ -77,3 +77,9 @@ fn sum_of_a_row_containing_a_table_is_an_error() {
         .err
         .contains("Attempted to compute the sum of a value that cannot be summed"));
 }
+
+#[test]
+fn const_sum() {
+    let actual = nu!("const SUM = [1 3] | math sum; $SUM");
+    assert_eq!(actual.out, "4");
+}

crates/nu-command/tests/commands/math/variance.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn const_variance() {
+    let actual = nu!("const VAR = [1 2 3 4 5] | math variance; $VAR");
+    assert_eq!(actual.out, "2");
+}