Check code examples

A lot of the new code blocks added in https://github.com/DioxusLabs/docsite/pull/532 were not added to example folder which means they are not formatted or checked to compile. Checking the examples would catch errors like [this](https://dioxuslabs.com/learn/0.7/essentials/basics/effects#derived-state-with-memo) broken codeblock in the effects section:

```rust
let mut loading = use_signal(|| false);
let mut loading_text = use_signal(|| "loading".to_string());

let subheading = use_memo(move || {
if load() && load_text() == "loading" {
return "The state is loading"
};

"The state is not loading"
});

rsx! {
h1 { "{subheading}" }
}
```

Review the code blocks added in pull request 532 and compare them with the example folder, starting with the broken Effects example at the linked documentation page. Check that each relevant block has a corresponding example that is formatted and compiles, including the derived-state-with-memo example.

Written by the indexing model from the issue text.