Change expected type for derived FromValue implementations via attribute (#13647)

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# Description
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In this PR I expanded the helper attribute `#[nu_value]` on
`#[derive(FromValue)]`. It now allows the usage of `#[nu_value(type_name
= "...")]` to set a type name for the `FromValue::expected_type`
implementation. Currently it only uses the default implementation but
I'd like to change that without having to manually implement the entire
trait on my own.

# User-Facing Changes
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helps us keep track of breaking changes. -->
Users that derive `FromValue` may now change the name of the expected
type.

# Tests + Formatting
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I added some tests that check if this feature work and updated the
documentation about the derive macro.

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

# After Submitting
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crates/nu-protocol/src/value/from_value.rs

@@ -34,10 +34,14 @@ use std::{
 /// [`#[serde(rename_all = "...")]`](https://serde.rs/container-attrs.html#rename_all) are valid
 /// here.
 ///
+/// Additionally, you can use `#[nu_value(type_name = "...")]` in the derive macro to set a custom type name
+/// for `FromValue::expected_type`. This will result in a `Type::Custom` with the specified type name.
+/// This can be useful in situations where the default type name is not desired.
+///
 /// ```
 /// # use nu_protocol::{FromValue, Value, ShellError};
 /// #[derive(FromValue, Debug, PartialEq)]
-/// #[nu_value(rename_all = "COBOL-CASE")]
+/// #[nu_value(rename_all = "COBOL-CASE", type_name = "birb")]
 /// enum Bird {
 ///     MountainEagle,
 ///     ForestOwl,
@@ -48,6 +52,11 @@ use std::{
 ///     Bird::from_value(Value::test_string("RIVER-DUCK")).unwrap(),
 ///     Bird::RiverDuck
 /// );
+///
+/// assert_eq!(
+///     &Bird::expected_type().to_string(),
+///     "birb"
+/// );
 /// ```
 pub trait FromValue: Sized {
     // TODO: instead of ShellError, maybe we could have a FromValueError that implements Into<ShellError>

crates/nu-protocol/src/value/test_derive.rs

@@ -494,3 +494,24 @@ fn bytes_roundtrip() {
         .into_test_value();
     assert_eq!(expected, actual);
 }
+
+#[test]
+fn struct_type_name_attr() {
+    #[derive(FromValue, Debug)]
+    #[nu_value(type_name = "struct")]
+    struct TypeNameStruct;
+
+    assert_eq!(
+        TypeNameStruct::expected_type().to_string().as_str(),
+        "struct"
+    );
+}
+
+#[test]
+fn enum_type_name_attr() {
+    #[derive(FromValue, Debug)]
+    #[nu_value(type_name = "enum")]
+    struct TypeNameEnum;
+
+    assert_eq!(TypeNameEnum::expected_type().to_string().as_str(), "enum");
+}