Reformat SPI flash sources and flashcode.h

Update formatting and style across lib-flash/src/spi/spi_flash.cpp and lib-flashcode/include/flashcode.h: bump copyright year to 2026, normalize spacing/indentation, unify pointer/type spacing, reformat constexpr table entries, compact enums/classes and namespace braces in header, and a small identifier rename (nRemainLength -> kRemainLength). These are non-functional style/cleanup changes to improve consistency and readability.

Author: vanvught