[Task] Optimize the code formatting settings

### Search before asking

- [x] I searched in the [issues](https://github.com/fast-excel/fastexcel/issues) and found nothing similar.

### Motivation

Although we have introduced the `spotless` plugin for automated code formatting, I recommend removing the `.editorconfig` files from the repository as they cannot replace code formatting.

We should continue using the `checkstyle` plugin for local development, and optimize code style configuration.

### Proposal

- Re-reference the `Checkstyle` plugin and add usage instructions for this plugin to the documentation.
- Optimize Spotless configuration.
- Fix the formatting style in the historical code.