Function parse 

pub fn parse(bytes: &[u8]) -> Result<(Cartridge, Box<dyn Mapper>), RomError>

Parse an iNES 1.0 / NES 2.0 ROM file.

Validates the magic, detects the format, applies the appropriate sizing rules, slices out the trainer (if any), PRG-ROM, and CHR-ROM, and returns a fully populated Cartridge plus a constructed dyn Mapper ready for the bus to consume.

Errors

• RomError::Truncated if the file is shorter than the declared sections.
• RomError::BadMagic if the first 4 bytes are not "NES\x1A".
• RomError::UnsupportedMapper if the mapper id is outside the supported set listed at crate level.
• RomError::InvalidConfig for inconsistent header fields (e.g., exponent overflow).