Apply nightly clippy fixes (#11083)

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Clippy fixes for rust 1.76.0-nightly

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

N/A
# Tests + Formatting
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crates/nu-cmd-dataframe/src/dataframe/eager/drop.rs

@@ -68,7 +68,7 @@ fn command(
     let df = NuDataFrame::try_from_pipeline(input, call.head)?;
 
     let new_df = col_string
-        .get(0)
+        .first()
         .ok_or_else(|| {
             ShellError::GenericError(
                 "Empty names list".into(),

crates/nu-cmd-dataframe/src/dataframe/eager/sql_context.rs

@@ -29,7 +29,7 @@ impl SQLContext {
     fn execute_select(&self, select_stmt: &Select) -> Result<LazyFrame, PolarsError> {
         // Determine involved dataframe
         // Implicit join require some more work in query parsers, Explicit join are preferred for now.
-        let tbl = select_stmt.from.get(0).ok_or_else(|| {
+        let tbl = select_stmt.from.first().ok_or_else(|| {
             PolarsError::ComputeError(ErrString::from("No table found in select statement"))
         })?;
         let mut alias_map = HashMap::new();
@@ -37,7 +37,7 @@ impl SQLContext {
             TableFactor::Table { name, alias, .. } => {
                 let tbl_name = name
                     .0
-                    .get(0)
+                    .first()
                     .ok_or_else(|| {
                         PolarsError::ComputeError(ErrString::from(
                             "No table found in select statement",
@@ -182,7 +182,7 @@ impl SQLContext {
             ))
         } else {
             let ast = ast
-                .get(0)
+                .first()
                 .ok_or_else(|| PolarsError::ComputeError(ErrString::from("No statement found")))?;
             Ok(match ast {
                 Statement::Query(query) => {

crates/nu-cmd-dataframe/src/dataframe/values/nu_dataframe/mod.rs

@@ -325,7 +325,7 @@ impl NuDataFrame {
         let series = self
             .df
             .get_columns()
-            .get(0)
+            .first()
             .expect("We have already checked that the width is 1");
 
         Ok(series.clone())

crates/nu-cmd-dataframe/src/dataframe/values/utils.rs

@@ -11,7 +11,7 @@ pub(crate) fn convert_columns(
 ) -> Result<(Vec<Spanned<String>>, Span), ShellError> {
     // First column span
     let mut col_span = columns
-        .get(0)
+        .first()
         .ok_or_else(|| {
             ShellError::GenericError(
                 "Empty column list".into(),
@@ -54,7 +54,7 @@ pub(crate) fn convert_columns_string(
 ) -> Result<(Vec<String>, Span), ShellError> {
     // First column span
     let mut col_span = columns
-        .get(0)
+        .first()
         .ok_or_else(|| {
             ShellError::GenericError(
                 "Empty column list".into(),