`dx fmt` inserts Unix newlines into Windows format files

**Problem**

When coding on Windows, files usually have the `\r\n` line endings. (Madness, I know!). Running `dx fmt` on either a single file or a group of files, replaces line endings with `\n` (Unix style) only.

If `dx fmt` is run without the `--all-code` flag, this results in mixed line endings - the `rsx!` blocks have `\n` whereas the rest of the file will continue to have `\r\n`.

When run with `--all-code` the entire file switches to `\n`.

Either way Git madness results.

I'm genuinely surprised this doesn't seem to have been reported before! I searched all issues with the word "fmt" in, so I apologise if I missed it.

**Steps To Reproduce**

Steps to reproduce the behavior:

- Create a new Rust file with an rsx block
- Run `dx fmt` on the file.
- Line endings are changed

**Expected behavior**

Line endings respect the existing file conventions, or failing that then the user should be able to specify the desired line endings.

**Screenshots**

n/a

**Environment:**

- Dioxus version: `dx --version > dioxus 0.6.3 (fc1f1c2)`
- Rust version: 1.89 stable
- OS info: Windows (normal Windows, not WSL)
- App platform: n/a

**Questionnaire**

- [x] I'm interested in fixing this myself but don't know where to start.
- [ ] I would like to fix and I have a solution.
- [ ] I don't have time to fix this right now, but maybe later.