to <format>: preserve round float numbers' type (#16016)

- fixes #16011

# Description
`Display` implementation for `f64` omits the decimal part for round
numbers, and by using it we did the same.
This affected:
- conversions to delimited formats: `csv`, `tsv`
- textual formats: `html`, `md`, `text`
- pretty printed `json` (`--raw` was unaffected)
- how single float values are displayed in the REPL

> [!TIP]
> This PR fixes our existing json pretty printing implementation.
> We can likely switch to using serde_json's impl using its
PrettyFormatter which allows arbitrary indent strings.

# User-Facing Changes
- Round trips through `csv`, `tsv`, and `json` preserve the type of
round floats.
- It's always clear whether a number is an integer or a float in the
REPL
  ```nushell
  4 / 2
  # => 2  # before: is this an int or a float?

  4 / 2
  # => 2.0  # after: clearly a float
  ``` 

# Tests + Formatting
Adjusted tests for the new behavior.

- 🟢 toolkit fmt
- 🟢 toolkit clippy
- 🟢 toolkit test
- 🟢 toolkit test stdlib

# After Submitting
N/A

---------

Co-authored-by: Bahex <17417311+Bahex@users.noreply.github.com>

crates/nu-command/tests/format_conversions/json.rs

@@ -17,6 +17,17 @@ fn table_to_json_text_and_from_json_text_back_into_table() {
     assert_eq!(actual.out, "markup");
 }
 
+#[test]
+fn table_to_json_float_doesnt_become_int() {
+    let actual = nu!(pipeline(
+        r#"
+            [[a]; [1.0]] | to json | from json | get 0.a | describe
+        "#
+    ));
+
+    assert_eq!(actual.out, "float")
+}
+
 #[test]
 fn from_json_text_to_table() {
     Playground::setup("filter_from_json_test_1", |dirs, sandbox| {