optimize/clean up a few of the table changes (#11076)

# Description

@sholderbach pointed out some places that I could help improve the code
in the table command changes. This PR tries to implement those.

# User-Facing Changes
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crates/nu-command/src/viewers/table.rs

@@ -321,21 +321,16 @@ fn get_theme_flag(
     state: &EngineState,
     stack: &mut Stack,
 ) -> Result<Option<TableMode>, ShellError> {
-    let theme_name = call.get_flag(state, stack, "theme")?;
+    call.get_flag(state, stack, "theme")?
-    theme_name
+        .map(|theme: String| {
-        .clone()
+            TableMode::from_str(&theme).map_err(|err| ShellError::CantConvert {
-        .map(|theme: String| TableMode::from_str(&theme))
-        .transpose()
-        .map_err(|err| ShellError::CantConvert {
                 to_type: String::from("theme"),
                 from_type: String::from("string"),
                 span: call.span(),
-            help: Some(format!(
+                help: Some(format!("{}, but found '{}'.", err, theme)),
-                "{}, but found '{}'.",
-                String::from(err),
-                theme_name.unwrap_or("".to_string())
-            )),
             })
+        })
+        .transpose()
 }
 
 struct CmdInput<'a> {

crates/nu-protocol/src/config/table.rs

@@ -11,7 +11,6 @@ pub enum TableMode {
     Compact,
     WithLove,
     CompactDouble,
-    Default,
     #[default]
     Rounded,
     Reinforced,
@@ -36,7 +35,7 @@ impl FromStr for TableMode {
             "compact" => Ok(Self::Compact),
             "with_love" => Ok(Self::WithLove),
             "compact_double" => Ok(Self::CompactDouble),
-            "default" => Ok(Self::Rounded),
+            "default" => Ok(TableMode::default()),
             "rounded" => Ok(Self::Rounded),
             "reinforced" => Ok(Self::Reinforced),
             "heavy" => Ok(Self::Heavy),
@@ -62,7 +61,6 @@ impl ReconstructVal for TableMode {
                 TableMode::Compact => "compact",
                 TableMode::WithLove => "with_love",
                 TableMode::CompactDouble => "compact_double",
-                TableMode::Default => "rounded",
                 TableMode::Rounded => "rounded",
                 TableMode::Reinforced => "reinforced",
                 TableMode::Heavy => "heavy",

crates/nu-table/src/common.rs

@@ -182,7 +182,6 @@ pub fn load_theme(mode: TableMode) -> TableTheme {
         TableMode::Compact => TableTheme::compact(),
         TableMode::WithLove => TableTheme::with_love(),
         TableMode::CompactDouble => TableTheme::compact_double(),
-        TableMode::Default => TableTheme::rounded(),
         TableMode::Rounded => TableTheme::rounded(),
         TableMode::Reinforced => TableTheme::reinforced(),
         TableMode::Heavy => TableTheme::heavy(),