Implement scaling logic

[malikalhack]

Apply voltage/timebase scaling to raw sample values

[malikalhack]

Placement of the code:
The new core module, currently an empty stub, contains only math functions and has no dependencies on OpenGL, ImGui, or USB. The render directory is intentionally left empty—it's reserved for future rendering code that will use this math.

[malikalhack]

• waveform_parser.h: SWaveformSamples stores raw ADC bytes (0–255) for two channels, without units.
• main.cpp: The UI already stores timebase (index 0-9) and voltsPerDivision[2] (index 0-7) as presentation-only state, plus duplicate text arrays timebases[] / voltageScales[] - the numerical values for these divisions are not yet present anywhere.
• Drawing grid: divisionsX = 10, divisionsY = 8 (main.cpp, drawOscilloscopeGrid).
• In glbox.h and hantekdsoathread.h, I found legacy markup constants: DIVS_TIME=10, DIVS_VOLTAGE=8, VOLTAGE_SCALE=256 (8-bit ADC), and the formula value - VOLTAGE_SCALE/2, scaled as DIVS_VOLTAGE/VOLTAGE_SCALE- i.e., center 128, 32 ADC counts per division. I'll use this formula as a reference without copying the code 1:1.
• Actual plotting (drawing the waveform) is a separate future task (fixed in HISTORY.md). I'm not doing it in this assignment; I'll just provide the pure math + a minimal proof via the status line (similar to what was previously done for the ring buffer).