[BUG] extra memory copy in bitmap operate

[stdpain]

Describe the bug

When we traverse the bitmap value, there may be performance or memory issues due to the extra memory copies.
It was caused by mismatched lambda expression parameters
eg:

#include <algorithm>
#include <iostream>
#include <map>

struct MC {
    MC() = default;
    MC(const MC& r) { std::cout << "call copy construct" << std::endl; }
    size_t write(char*) const { return 0; }
    int ans;
};

int main() {
    MC mc0;
    std::map<int, MC> st;
    using iter = std::map<int, MC>::iterator;
    st[0] = mc0;
    st[1] = mc0;
    std::cout << "start test" << std::endl;
    char mem_buffer[4096];
    char* buf = mem_buffer;
    std::for_each(st.cbegin(), st.cend(), [&buf](const std::pair<const int, MC>& map_entry) {
        buf += map_entry.second.write(buf);
    });
    std::cout << "start test 2" << std::endl;
    std::for_each(st.cbegin(), st.cend(), [&buf](const std::pair<int, MC>& map_entry) {
        buf += map_entry.second.write(buf);
    });

    return 0;
}

output:

start test
start test 2
call copy construct
call copy construct

so we should make std::pair<uint32_t,RoarMap> to std::pair<const uint32_t,RoarMap>