Backport: Add header guards and clean up Button self-qualification

[livingkurt]

Summary

These are small cleanup changes identified during the RAII branch review (PR #151) that apply cleanly to master and reduce the diff size of the RAII branch when they're merged here first.

• Add proper header guards to Button.h, Helios.h, ColorConstants.h, and Random.h. The first two had no include guard at all, the latter two used non-standard #pragma once.
• Remove unnecessary Button:: self-qualification on static method calls within Button.cpp (holdPressing, processPreInput, processPostInput). These are calls to the class's own static members and don't need the class prefix.
• Extract repeated Time::getCurtime() calls into a const local variable in Button::update() for clarity (the compiler likely optimizes this already, but the old AVR compiler may benefit).

Test plan

• CLI builds with zero warnings
• All 506 tests pass

Made with Cursor

[Unreal-Dan]

Okay this is my first experience with cursor, this is really cool lol

I am curious though can it actually tell if the total size is smaller? It would need to look at this output of this build step:

master

Sketch uses 8010 bytes (97.78%) of program storage space. Maximum is 8192 bytes. (Hex: 1f4a/2000)
Global variables use 276 bytes (53.91%) of dynamic memory, leaving 236 bytes for local variables. Maximum is 512 bytes. (Hex: 114/200)
== Success building Helios v1.4.0 ==

This one

Sketch uses 7938 bytes (96.90%) of program storage space. Maximum is 8192 bytes. (Hex: 1f02/2000)
Global variables use 276 bytes (53.91%) of dynamic memory, leaving 236 bytes for local variables. Maximum is 512 bytes. (Hex: 114/200)
== Success building Helios v1.4.0 ==

So it's definitely smaller, which makes sense, but I'm curious would Cursor know if it wasn't?

Other than this question, changeset looks good to me and definitely fixes the issues

[Unreal-Dan]

Can confirm same size before and after removing the call to Helios::wakeup() in the ISR, therefore it was never needed and logically doesn't make sense for embedded.

Same size: 96.90% and globals 53.91%

Sketch uses 7938 bytes (96.90%) of program storage space. Maximum is 8192 bytes. (Hex: 1f02/2000)
Global variables use 276 bytes (53.91%) of dynamic memory, leaving 236 bytes for local variables. Maximum is 512 bytes. (Hex: 114/200)
== Success building Helios v1.4.0 ==