Function is_wav_path

app/cli/batch.cpp:19–25

namespace {

bool is_wav_path(const std::filesystem::path & path) {
    std::string ext = path.extension().string();
    std::transform(ext.begin(), ext.end(), ext.begin(), [](unsigned char ch) {
        return static_cast<char>(std::tolower(ch));
    });
    return ext == ".wav";
}

std::string lowercase_extension(const std::filesystem::path & path) {
    std::string ext = path.extension().string();