Wrong double slash rules in mod_rewite rules in Super Cache

### Impacted plugin

Super Cache

### Quick summary

Super Cache writes rewrite rules in .htaccess for Apache. It seems to handle case for trailing slashes and double slashes in Request_URI with these rules:

```
AddDefaultCharset UTF-8
RewriteCond %{REQUEST_URI} !^.*[^/]$
RewriteCond %{REQUEST_URI} !^.*//.*$
```

However in Apache, the REQUEST_URI variable is converted to single slashes by default.

To check double slashes, you need to use `%{THE_REQUEST}`

### Steps to reproduce

- Check if a page is cached by checking the cached file location.
- Load the page from a browser with browser caches clear.
- Check that the page is not redirected.

### A clear and concise description of what you expected to happen.

Pages with double slash should be redirected to one with single slash

### What actually happened

No redirect happens because of the rewrite rules should have used "the_request"

### Impact

Most (> 50%)

### Available workarounds?

Yes, easy to implement

### Platform (Simple and/or Atomic)

_No response_

### Logs or notes

_No response_

Locate the Super Cache code that writes the .htaccess rewrite rules, then reproduce the request with a double slash and inspect how Apache exposes REQUEST_URI versus THE_REQUEST. Done means the generated rules detect and redirect double-slash paths while preserving the existing trailing-slash behavior.

Written by the indexing model from the issue text.