`\\` is translated inconsitently

I have try to prase markdown with the pulldown-cmark crate and to convert it back, using this crate.
But `\\` is translated back inconsistent. At some point `\\` is converted to `\` and at other points it is still `\\`.
For Example
This line occurs in my markdown files multiple times `\\( \int x dx = \frac{x^2}{2} + C \\)`.
The first time it stay the same, all other time it result in `\( \int x dx = \frac{x^2}{2} + C \)`,
so the mathjax expression are not render by the mdbook.

code:
```rust
let markdown_copy = markdown.clone();
eprintln!("{markdown_copy}");
let parser = pulldown_cmark::Parser::new(&markdown_copy);
let mut in_code_block = false;
let iter = parser.into_iter().map(|f| {
eprintln!("in {f:?}");
let f =match f {
Event::Text(text) => Event::Text(CowStr::from(text.replace("=>", "⇒"))),
Event::Start(Tag::CodeBlock(value)) => {in_code_block = true; Event::Start(Tag::CodeBlock(value))},
Event::End(Tag::CodeBlock(value)) => {in_code_block = false; Event::Start(Tag::CodeBlock(value))}
f => f
};
eprintln!("out {f:?}");
f
});
let mut output = String::new();
pulldown_cmark_to_cmark::cmark(iter, &mut output).unwrap();
eprintln!("{output}");
```
output:
[input.md](https://github.com/Byron/pulldown-cmark-to-cmark/files/13460682/input.md)
```
in Start(Heading(H1, None, []))
out Start(Heading(H1, None, []))
in Text(Borrowed("Chapter 1"))
out Text(Boxed("Chapter 1"))
in End(Heading(H1, None, []))
out End(Heading(H1, None, []))
in Start(Paragraph)
out Start(Paragraph)
in Text(Borrowed("hello world."))
out Text(Boxed("hello world."))
in SoftBreak
out SoftBreak
in Text(Borrowed("This is a "))
out Text(Boxed("This is a "))
in Start(Link(Inline, Borrowed("https://duckduckgo.com"), Borrowed("")))
out Start(Link(Inline, Borrowed("https://duckduckgo.com"), Borrowed("")))
in Text(Borrowed("duck"))
out Text(Boxed("duck"))
in End(Link(Inline, Borrowed("https://duckduckgo.com"), Borrowed("")))
out End(Link(Inline, Borrowed("https://duckduckgo.com"), Borrowed("")))
in SoftBreak
out SoftBreak
in Text(Borrowed("arrows: -> = >"))
out Text(Boxed("arrows: -> = >"))
in SoftBreak
out SoftBreak
in Text(Borrowed("ee"))
out Text(Boxed("ee"))
in End(Paragraph)
out End(Paragraph)
in Start(Paragraph)
out Start(Paragraph)
in Text(Borrowed("\\( \\int x dx = \\frac{x^2}{2} + C "))
out Text(Boxed("\\( \\int x dx = \\frac{x^2}{2} + C "))
in Text(Borrowed("\\)"))
out Text(Boxed("\\)"))
in End(Paragraph)
out End(Paragraph)
in Start(CodeBlock(Fenced(Borrowed(""))))
out Start(CodeBlock(Fenced(Borrowed(""))))
in Text(Borrowed("this arrows should not be replaced:\n-> =>\n"))
out Text(Boxed("this arrows should not be replaced:\n-> ⇒\n"))
in End(CodeBlock(Fenced(Borrowed(""))))
out Start(CodeBlock(Fenced(Borrowed(""))))
in Start(Paragraph)
out Start(Paragraph)
in Text(Borrowed("\\( \\int x dx = \\frac{x^2}{2} + C "))
out Text(Boxed("\\( \\int x dx = \\frac{x^2}{2} + C "))
in Text(Borrowed("\\)"))
out Text(Boxed("\\)"))
in End(Paragraph)
out End(Paragraph)
in Start(Paragraph)
out Start(Paragraph)
in Text(Borrowed("this should also not be replaced "))
out Text(Boxed("this should also not be replaced "))
in Code(Borrowed("->"))
out Code(Borrowed("->"))
in Text(Borrowed(" "))
out Text(Boxed(" "))
in Code(Borrowed("=>"))
out Code(Borrowed("=>"))
in Text(Borrowed(". "))
out Text(Boxed(". "))
in End(Paragraph)
out End(Paragraph)
in Start(Paragraph)
out Start(Paragraph)
in Text(Borrowed("\\"))
out Text(Boxed("\\"))
in Text(Borrowed("["))
out Text(Boxed("["))
in Text(Borrowed(" \\mu = \\frac{1}{N} \\sum"))
out Text(Boxed(" \\mu = \\frac{1}{N} \\sum"))
in Text(Borrowed("_"))
out Text(Boxed("_"))
in Text(Borrowed("{i=0} x_i \\Rightarrow"))
out Text(Boxed("{i=0} x_i \\Rightarrow"))
in Text(Borrowed("\\"))
out Text(Boxed("\\"))
in Text(Borrowed("]"))
out Text(Boxed("]"))
in End(Paragraph)
out End(Paragraph)
```
[output.md](https://github.com/Byron/pulldown-cmark-to-cmark/files/13460688/output.md)

I war forced to upload the markdowns as file, because otherwise github has try to interpret it.