Fix encode base64 type signature and examples (#7515)

# Description

See title.

# User-Facing Changes

See title.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/strings/encode_decode/base64.rs

@@ -161,7 +161,7 @@ fn action(
         }
         other => Value::Error {
             error: ShellError::TypeMismatch(
-                format!("value is {}, not string", other.get_type()),
+                format!("string or binary, not {}", other.get_type()),
                 other.span().unwrap_or(command_span),
             ),
         },

crates/nu-command/src/strings/encode_decode/encode_base64.rs

@@ -15,7 +15,10 @@ impl Command for EncodeBase64 {
 
     fn signature(&self) -> Signature {
         Signature::build("encode base64")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Binary, Type::String),
+            ])
             .vectorizes_over_list(true)
             .named(
                 "character-set",
@@ -33,18 +36,23 @@ impl Command for EncodeBase64 {
     }
 
     fn usage(&self) -> &str {
-        "Base64 encode a value"
+        "Encode a string or binary value using Base64"
     }
 
     fn examples(&self) -> Vec<Example> {
         vec![
             Example {
-                description: "Base64 encode a string with default settings",
+                description: "Encode binary data",
+                example: "0x[09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0] | encode base64",
+                result: Some(Value::string("CfkRAp1041vYQVbFY1aIwA==", Span::test_data())),
+            },
+            Example {
+                description: "Encode a string with default settings",
                 example: "'Some Data' | encode base64",
                 result: Some(Value::string("U29tZSBEYXRh", Span::test_data())),
             },
             Example {
-                description: "Base64 encode a string with the binhex character set",
+                description: "Encode a string with the binhex character set",
                 example: "'Some Data' | encode base64 --character-set binhex",
                 result: Some(Value::string(r#"7epXB5"%A@4J"#, Span::test_data())),
             },