150 improve ui

[AlixANNERAUD]

This pull request introduces a new symbols module to centralize and simplify the handling of LVGL symbol constants, refactors code to use this new module, and adds improvements to theming and styling in the graphics module. Additionally, it includes a minor fix in a task manager test.

Graphics Symbol Handling and Refactoring:

• Added a new symbols module (modules/graphics/src/symbols.rs) that provides safe, idiomatic Rust constants for all LVGL symbols as &CStr, replacing direct usage of raw LVGL constants throughout the codebase. [1] [2]
• Refactored all usages of LVGL symbol constants in file_manager.rs and layout.rs to use the new symbols module, improving code readability and safety. [1] [2] [3] [4] [5] [6] [7] [8] [9]

Graphics and Theming Enhancements:

• Added new constants for border width, radius, and padding in the theme module and refactored tabview, checkbox, list, and switch theming to use these constants, resulting in more consistent and maintainable styling. [1] [2] [3]
• Added a helper function lv_tabview_add_tab in lvgl.rs to encapsulate tab creation and ensure consistent tab button sizing. [1] [2]

Testing:

• Fixed a test in the task manager to correctly assert that completed child tasks are no longer present in the children list, removing a potentially misleading check on the initial count. [1] [2]

[codecov]

Codecov Report

❌ Patch coverage is 1.96078% with 100 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
modules/graphics/src/theme.rs	0.00%	82 Missing ⚠️
modules/graphics/src/lvgl.rs	0.00%	10 Missing ⚠️
executables/file_manager/src/file_manager.rs	0.00%	6 Missing ⚠️
executables/shell/graphical/src/layout.rs	0.00%	2 Missing ⚠️

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