Function preprocess_raw_contig 

pub fn preprocess_raw_contig(contig: &mut Vec<u8>)

Preprocess raw contig by converting ASCII characters to numeric codes

Matches C++ AGC’s preprocess_raw_contig() logic:

• Filters bytes with high bits set (>= 64, i.e., letter characters)
• Converts them using cnv_num lookup table
• Removes all other characters (like spaces, newlines)
• Uses loop unrolling for performance (processes 4 bytes at a time)

Arguments

• contig - Mutable vector to process in place

Behavior

• Modifies contig in place
• Resizes to contain only converted characters