Add .editorconfig for consistent code formatting (#38)

Xcode 16 added support for the [EditorConfig
standard](https://editorconfig.org/)[^1]. This allows a project/repo to
specify basic formatting rules so the editor can behave correctly.[^2]

> [!NOTE]
> You may need to quit and relaunch Xcode for it to pick up the
`.editorconfig` file after switching to a branch where it's present.[^3]

The added `.editorconfig` file contains:

```
# editorconfig.org
root = true

[*]
indent_style = space
indent_size = 2
trim_trailing_whitespace = true
insert_final_newline = true
```

- `root = true`: Specifies that this is the top-most .editorconfig file.
The file search will stop here.
- `indent_style = space`: Uses soft tabs (spaces) for indentation
instead of hard tabs.
- `indent_size = 2`: Sets the indentation to 2 columns.
- `trim_trailing_whitespace = true`: Removes any whitespace characters
preceding newline characters.
- `insert_final_newline = true`: Ensures the file ends with a newline
when saving.

These settings apply to all files in the project (`[*]`).

**This change make much easier the process of switch between projects
that use 2-space and 4-space indentation (what is quite common in your
community).**

[^1]: [Xcode 16 Beta 2 Release Notes–Source Editor New
Features](https://arc.net/l/quote/zuzqnfeq)
[^2]: Inspired by: [Add an EditorConfig
file](swiftlang/swift-syntax#2714)
[^3]: [Xcode 16 Beta 2 Release Notes–Source Editor Known
Issues](https://arc.net/l/quote/olmnhsqo)

.editorconfig

@@ -0,0 +1,9 @@
+# editorconfig.org
+
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true
+insert_final_newline = true