Update C++ license headers

[franzpoeschel]

The license headers have often been forgotten in PRs. This PR uses a little script to update this info in the C++ files.

The script:

#!/usr/bin/env bash

get_copyright_banner() {
    grep --color=never -zPo '/\*[\s\S]*?Copyright[\s\S]*?\*/'
}

author_names() {
    local name="$1"
    if [[ "$name" = "Axel Huebl" ]]; then
        echo "$name"
    elif [[ "$name" = "Ben Wibking" ]]; then
        echo "$name"
    elif [[ "$name" = "C0nsultant" ]]; then
        echo "Fabian Koller"
    elif [[ "$name" = "Carsten Fortmann-Grote" ]]; then
        echo "$name"
    elif [[ "$name" = "David Grote" ]]; then
        echo "$name"
    elif [[ "$name" = "Franz Pöschel" ]]; then
        echo "Franz Poeschel"
    elif [[ "$name" = "guj" ]]; then
        echo "Junmin Gu"
    elif [[ "$name" = "Ilian Kara-Mostefa" ]]; then
        echo "$name"
    elif [[ "$name" = "Jean Luca Bez" ]]; then
        echo "$name"
    elif [[ "$name" = "Junmin Gu" ]]; then
        echo "$name"
    elif [[ "$name" = "L. Diana Amorim" ]]; then
        echo "$name"
    elif [[ "$name" = "Luca Fedeli" ]]; then
        echo "$name"
    elif [[ "$name" = "Paweł Ordyna" ]]; then
        echo "Pawel Ordyna"
    elif [[ "$name" = "Richard Pausch" ]]; then
        echo "$name"
    elif [[ "$name" = "Ulrik Günther" ]]; then
        echo "Ulrik Guenther"
    fi
}

get_authors() {
    local file="$1"
    local authors
    mapfile -t authors < <(
        git blame -p "$file" |
            grep -E '^[^[:space:]]' |
            awk '$1 == "author"' |
            sort |
            uniq |
            sed 's|^author ||'
    )
    for name in "${authors[@]}"; do
        author_names "$name"
    done
}

include_author() {
    local copyright_banner="$1"
    local author="$2"
    if grep "$author" <<<"$copyright_banner" >/dev/null 2>&1; then
        echo "$copyright_banner"
        return
    fi
    echo "$copyright_banner" |
        sed -E "s|(Copyright .*)|\1, $author|" |
        sed -E 's|([0-9]{4}-)[0-9]{4}|\12025|' |
        sed -E 's| ([0-9]{4}) | \1-2025 |'
}

make_banner() {
    local authorstring="$(
        printf '%s\n' "$(
            IFS=,
            echo "${authors[*]}"
        )" | sed 's|,|, |g'
    )"
    cat <<EOF
/* Copyright 2025 ${authorstring}
 *
 * This file is part of openPMD-api.
 *
 * openPMD-api is free software: you can redistribute it and/or modify
 * it under the terms of of either the GNU General Public License or
 * the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * openPMD-api is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License and the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License
 * and the GNU Lesser General Public License along with openPMD-api.
 * If not, see <http://www.gnu.org/licenses/>.
 */
EOF
}

fix_file() {
    local filename="$1"
    local banner="$(get_copyright_banner <"$filename")"
    local authors
    mapfile -t authors < <(get_authors "$filename")
    if [[ -z "$banner" ]]; then
        local new_banner="$(
            make_banner "${authors[@]}" |
                sed -z 's|\n|\\n|g'
        )"
        sed -zi "s|^|$new_banner|" "$filename"
        return
    fi
    local original_banner="$banner"
    for author in "${authors[@]}"; do
        banner="$(include_author "$banner" "$author")"
    done
    old_single_line="$(
        grep Copyright <<<"$original_banner" |
            sed 's|\*|\\*|'
    )"
    new_single_line="$(grep Copyright <<<"$banner")"
    sed -i "s|${old_single_line}|${new_single_line}|" "$filename"
}