Add ShiftRegister74HC595Helper for SPI-based shift register control

[j-heitz]

Issue #118

Summary

This PR introduces a new helper class [ShiftRegister74HC595Helper] that controls 74HC595 shift registers via SPI communication on Raspberry Pi devices. Also Introduces a [ShiftRegister74HC595HelperTest].

Changes

• New Class: [ShiftRegister74HC595Helper]
• Comprehensive Test: [ShiftRegister74HC595HelperTest]

Basic Operations:

• [shiftOut(byte)] - Write a byte value to the shift register
• [clear()] - Reset all outputs to LOW (0x00)
• [getState()]- Get current state of the shift register

Bit Manipulation:

• [setBit(int, boolean)] - Set or clear individual bits (0-7)
• [clearBit(int)] - Clear a specific bit

Error Handling:

• Proper exception handling for SPI communication failures
• Input validation for bit indices (0-7 range)
• Comprehensive logging using SLF4J

Technical Details

• Uses Pi4J SPI interface for hardware communication
• Includes proper null checking and validation
• Comprehensive unit tests with Mockito for SPI mocking

Testing

• Valid operations and edge cases
• Exception handling scenarios
• State management verification
• Input validation

[leandrumartin]

The helper class itself should also have a Javadoc comment right above its declaration. Everything else looks good.