refactor: extract some logic classes into core

[andre-stefanov]

Phase 1: Extract pure domain logic into core

Summary

Extracts the pure (non-Arduino) arithmetic subsets of the firmware's core data types and algorithms into core, making them host-testable via the native PlatformIO environment. The original src files become thin overlays that inherit from the core versions and add only Arduino-dependent methods (ParseFromMeade, ToString). Zero behavior change — all 5 boards build green.

Architecture

src/core/
├── types/                     # Pure data containers (no Arduino)
│   ├── DayTime.hpp/.cpp       # 24h time arithmetic, formatString
│   ├── RightAscension.hpp/.cpp# 0–24h RA coordinate (wrapping)
│   ├── Declination.hpp/.cpp   # ±180° DEC coordinate (clamping)
│   ├── Latitude.hpp/.cpp      # ±90° latitude (clamping)
│   └── Longitude.hpp/.cpp     # ±180° longitude (wrapping)
├── SiderealClock.hpp/.cpp     # LST/HA calculation (theta, delta-JD)
├── CalendarMath.hpp/.cpp      # Date arithmetic with leap-year rules
├── CoordinateMath.hpp/.cpp    # Meridian-flip solution selector
├── CoordinateFormatter.hpp/.cpp# RA/DEC char-buffer formatting
└── EepromLayout.hpp           # Magic markers, flags, layout constants

Each src originals (DayTime, Declination, Latitude, Longitude) is now a thin overlay:

// src/DayTime.hpp
class DayTime : public core::DayTime {
    using core::DayTime::DayTime;  // inherit constructors
    virtual const char *ToString() const;
    static DayTime ParseFromMeade(String const &s);
};

New files

#	File
6	src/core/types/{DayTime,RightAscension,Declination,Latitude,Longitude}.{hpp,cpp}
4	src/core/{SiderealClock,CalendarMath,CoordinateMath,CoordinateFormatter}.{hpp,cpp}
1	EepromLayout.hpp
2	src/{RightAscension}.{hpp,cpp} (new overlay)
10	unit_tests/test_core/{test_sidereal,test_calendar,test_coordinate_math,test_coordinate_formatter,test_eeprom_layout,types/test_daytime,types/test_declination,types/test_latitude,types/test_longitude,types/test_right_ascension}.cpp

Modified files

#	File	Change
8	src/{DayTime,Declination,Latitude,Longitude}.{hpp,cpp}	Converted to thin overlays; pure methods removed
1	Sidereal.cpp	Delegates to core::SiderealClock

Test results

258 test cases: 258 succeeded (188 existing + 70 new)

All 5 board matrix builds green (ramps, mksgenlv21, mksgenlv2, mksgenlv1, esp32, oaeboardv1).

Key decisions

• Extract-before-test: src root files transitively include <Arduino.h> via inc/Globals.hpp and are untestable on native. Pure logic is extracted into core/ first, then tested.
• Thin overlays preserve back-compat: Originals #include the core version and add only String-dependent methods. No flag day.
• core namespace: All extracted types live in namespace core to avoid collisions with the overlay classes in the global namespace.
• core::RightAscension was added as a first-class RA coordinate type alongside Declination, replacing DayTime in CoordinateFormatter::formatRA(). Inheritance from DayTime is acknowledged as a transitional convenience — a composition-based design is planned for Phase 2.

What's next (Phase 2)

Introduce HAL interfaces (IStepperMotor, ISystemClock, IEeprom, …), domain ports (IClock, IPersistentStore, IStepperAxis, …), and adapters that bind ports to HAL. Wire Mount to use injected port pointers instead of concrete types.