No-bracket style

Make a no-bracket style calculator like i phone. But as brackets support is added, no need for this.

The issue mentions a 'no-bracket style calculator like iPhone' but says brackets support is already added, making the need unclear. Look at the existing calculator logic in the codebase, likely in a main Python file using Kivy. Determine how expression parsing currently works and what changes would enable a bracket-less input mode while maintaining BODMAS rules. Check if there are any tests for the calculator functionality to understand the expected behavior.

由索引模型根据 Issue 内容生成。