Rewrite packed file parser with finite state machines

[nanxstats]

Closes #14

This PR rewrites the packed file parser using finite state machines. The current implementation uses a stateful approach. The new implementation makes the parser easier to read and maintain.

Using the following shell script, I did some real-world tests to compare the pkglite unpack output directories (one or multiple) from this implementation and the existing implementation.

compare.sh

#!/bin/bash

function compute_md5 {
    md5 "$1" | awk '{print $4}'
}

function compare_directories {
    local dir1="$1"
    local dir2="$2"
    local mismatch_count=0

    IFS=$'\n' dir1_files=($(find "$dir1" -type f -o -type d | sort))
    IFS=$'\n' dir2_files=($(find "$dir2" -type f -o -type d | sort))

    # Normalize paths
    dir1_base_len=${#dir1}
    dir2_base_len=${#dir2}
    for i in "${!dir1_files[@]}"; do
        dir1_files[$i]="${dir1_files[$i]:$dir1_base_len}"
    done
    for i in "${!dir2_files[@]}"; do
        dir2_files[$i]="${dir2_files[$i]:$dir2_base_len}"
    done

    # Check if directory structures match
    if [ "${#dir1_files[@]}" -ne "${#dir2_files[@]}" ]; then
        echo "Directory structures differ."
        echo "Extra files or directories:" >&2
        diff <(printf "%s\n" "${dir1_files[@]}") <(printf "%s\n" "${dir2_files[@]}") | head -10 >&2
        exit 1
    fi

    for i in "${!dir1_files[@]}"; do
        if [ "${dir1_files[i]}" != "${dir2_files[i]}" ]; then
            echo "Mismatch in directory structure: ${dir1_files[i]} vs ${dir2_files[i]}"
            mismatch_count=$((mismatch_count + 1))
            if [ $mismatch_count -ge 10 ]; then break; fi
        fi
    done

    # Check file contents match
    for i in "${!dir1_files[@]}"; do
        local path1="$dir1/${dir1_files[i]}"
        local path2="$dir2/${dir2_files[i]}"

        # Skip directories
        if [ -d "$path1" ]; then
            continue
        fi

        if ! cmp -s "$path1" "$path2"; then
            echo "File content mismatch: $path1 vs $path2"
            mismatch_count=$((mismatch_count + 1))
            if [ $mismatch_count -ge 10 ]; then break; fi
        fi
    done

    if [ $mismatch_count -eq 0 ]; then
        echo "Directories are identical."
    else
        echo "Directories differ. See details above."
    fi
}

# Check arguments
if [ "$#" -ne 2 ]; then
    echo "Usage: $0 <directory1> <directory2>"
    exit 1
fi

# Compare directories
compare_directories "$1" "$2"

They are identical.