Add PartialEq derive to Order

[russellbanks]

This pull request adds a PartialEq derive on Order in byteorder.rs.

While Order is marked hidden in documentation, the below use case illustrates why it would be helpful for it to implement PartialEq:

use std::borrow::Cow;

use zerocopy::{ByteOrder, U16, U32, transmute_ref};

enum Value<'a, O: ByteOrder> {
    Word(Cow<'a, [U16<O>]>),
    DWord(Cow<'a, [U32<O>]>),
}

impl<'a, O: ByteOrder> Value<'a, O> {
    pub fn to<P: ByteOrder>(&self) -> Value<'a, P> {
        if O::ORDER == P::ORDER {
            return match self {
                Self::Word(words) => Value::Word(Cow::Borrowed(transmute_ref!(&**words))),
                Self::DWord(dwords) => Value::DWord(Cow::Borrowed(transmute_ref!(&**dwords))),
            };
        }

        match self {
            Self::Word(words) => Value::Word(Cow::Owned(
                words.into_iter().map(|word| U16::new(word.get())).collect(),
            )),
            Self::DWord(dwords) => Value::DWord(Cow::Owned(
                dwords
                    .into_iter()
                    .map(|dword| U32::new(dword.get()))
                    .collect(),
            )),
        }
    }
}

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.85%. Comparing base (3b29d25) to head (7be2d32).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3467   +/-   ##
=======================================
  Coverage   91.85%   91.85%           
=======================================
  Files          20       20           
  Lines        6093     6093           
=======================================
  Hits         5597     5597           
  Misses        496      496           

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