Address lints from clippy for beta/nightly (#5709)

* Fix clippy lints in tests

* Replace `format!` in `.push_str()` with `write!`

Stylistically that might be a bit rough but elides an allocation.

Fallibility of allocation is more explicit, but ignored with `let _ =`
like in the clippy example:

https://rust-lang.github.io/rust-clippy/master/index.html#format_push_string

* Remove unused lifetime

* Fix macro crate relative import

* Derive `Eq` for `PartialEq` with `Eq` members

https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

* Remove unnnecessary `.to_string()` for Cow<str>

* Remove `.to_string()` for `tendril::Tendril`

Implements `Deref<Target = str>`

crates/nu-protocol/src/ast/cell_path.rs

@@ -1,6 +1,7 @@
 use super::Expression;
 use crate::Span;
 use serde::{Deserialize, Serialize};
+use std::fmt::Write;
 
 #[derive(Debug, Clone, PartialOrd, Serialize, Deserialize)]
 pub enum PathMember {
@@ -32,7 +33,9 @@ impl CellPath {
                 output.push('.');
             }
             match elem {
-                PathMember::Int { val, .. } => output.push_str(&format!("{}", val)),
+                PathMember::Int { val, .. } => {
+                    let _ = write!(output, "{}", val);
+                }
                 PathMember::String { val, .. } => output.push_str(val),
             }
         }

crates/nu-protocol/src/ast/import_pattern.rs

@@ -3,21 +3,21 @@ use serde::{Deserialize, Serialize};
 use crate::{span, ModuleId, Span};
 use std::collections::HashSet;
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub enum ImportPatternMember {
     Glob { span: Span },
     Name { name: Vec<u8>, span: Span },
     List { names: Vec<(Vec<u8>, Span)> },
 }
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct ImportPatternHead {
     pub name: Vec<u8>,
     pub id: Option<ModuleId>,
     pub span: Span,
 }
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct ImportPattern {
     pub head: ImportPatternHead,
     pub members: Vec<ImportPatternMember>,

crates/nu-protocol/src/ast/operator.rs

@@ -54,13 +54,13 @@ impl Display for Operator {
     }
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, PartialOrd, Serialize, Deserialize)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Serialize, Deserialize)]
 pub enum RangeInclusion {
     Inclusive,
     RightExclusive,
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct RangeOperator {
     pub inclusion: RangeInclusion,
     pub span: Span,

crates/nu-protocol/src/signature.rs

@@ -11,6 +11,7 @@ use crate::PipelineData;
 use crate::ShellError;
 use crate::SyntaxShape;
 use crate::VarId;
+use std::fmt::Write;
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct Flag {
@@ -36,7 +37,7 @@ pub struct PositionalArg {
     pub default_value: Option<Expression>,
 }
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub enum Category {
     Default,
     Conversions,
@@ -345,7 +346,7 @@ impl Signature {
         }
 
         if let Some(rest) = &self.rest_positional {
-            one_liner.push_str(&format!("...{}", get_positional_short_name(rest, false)));
+            let _ = write!(one_liner, "...{}", get_positional_short_name(rest, false));
         }
 
         // if !self.subcommands.is_empty() {

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

@@ -1,6 +1,6 @@
 use serde::{Deserialize, Serialize};
 
-#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 pub enum Unit {
     // Filesize units: metric
     Byte,