chore: Enable assigning_clones clippy lint (#20670)

## Which issue does this PR close?

N/A

## Rationale for this change

The `assigning_clones` clippy lint seems marginally useful. Enabling it
for the whole workspace only catches a few places, but they are all
coding patterns that could be improved.

## What changes are included in this PR?

- Enable `assigning_clones` clippy lint as a workspace-level warning
- Fix existing lint violations (no false positives)

## Are these changes tested?

Yes, covered by existing tests. This is a mechanical refactor that does
not change behavior.

## Are there any user-facing changes?

No.

Author: neilconway

Cargo.toml

@@ -208,6 +208,7 @@ inefficient_to_string = "warn"
 needless_pass_by_value = "warn"
 # https://github.com/apache/datafusion/issues/18881
 allow_attributes = "warn"
+assigning_clones = "warn"
 
 [workspace.lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = [

datafusion/common/src/config.rs

@@ -2711,10 +2711,7 @@ impl From<&Arc<FileEncryptionProperties>> for ConfigFileEncryptionProperties {
                 },
             );
         }
-        let mut aad_prefix: Vec<u8> = Vec::new();
-        if let Some(prefix) = f.aad_prefix() {
-            aad_prefix = prefix.clone();
-        }
+        let aad_prefix = f.aad_prefix().cloned().unwrap_or_default();
         ConfigFileEncryptionProperties {
             encrypt_footer: f.encrypt_footer(),
             footer_key_as_hex: hex::encode(f.footer_key()),
@@ -2852,10 +2849,7 @@ impl From<&Arc<FileDecryptionProperties>> for ConfigFileDecryptionProperties {
             column_decryption_properties.insert(column_name.clone(), props);
         }
 
-        let mut aad_prefix: Vec<u8> = Vec::new();
-        if let Some(prefix) = f.aad_prefix() {
-            aad_prefix = prefix.clone();
-        }
+        let aad_prefix = f.aad_prefix().cloned().unwrap_or_default();
         ConfigFileDecryptionProperties {
             footer_key_as_hex: hex::encode(
                 f.footer_key(None).unwrap_or_default().as_ref(),

datafusion/physical-plan/src/aggregates/mod.rs

@@ -1429,7 +1429,7 @@ impl ExecutionPlan for AggregateExec {
             Arc::clone(&self.schema),
         )?;
         me.limit_options = self.limit_options;
-        me.dynamic_filter = self.dynamic_filter.clone();
+        me.dynamic_filter.clone_from(&self.dynamic_filter);
 
         Ok(Arc::new(me))
     }

datafusion/physical-plan/src/display.rs

@@ -734,13 +734,14 @@ impl TreeRenderVisitor<'_, '_> {
                 if let Some(node) = root.get_node(x, y) {
                     write!(self.f, "{}", Self::VERTICAL)?;
 
-                    // Rigure out what to render.
-                    let mut render_text = String::new();
-                    if render_y == 0 {
-                        render_text = node.name.clone();
+                    // Figure out what to render.
+                    let mut render_text = if render_y == 0 {
+                        node.name.clone()
                     } else if render_y <= extra_info[x].len() {
-                        render_text = extra_info[x][render_y - 1].clone();
-                    }
+                        extra_info[x][render_y - 1].clone()
+                    } else {
+                        String::new()
+                    };
 
                     render_text = Self::adjust_text_for_rendering(
                         &render_text,