Add partial base64 in-place encoding support

[Mis1eader-dev]

This PR allows for encoding a sequence of bytes, which does not exceed 12 bytes, in-place.
Added the declaration of another base64 encoding function that will do in-place encoding but with dynamic allocation.
Tried as much as I could to stick to the old implementation, had to make some structured changes to make it work for in-place encoding.

Replaced .resize() calls as they were allocating more than they needed in terms of capacity. Use this sample code to check out this change:

int main()
{
    constexpr auto len = 20;
    string s1(len, '0');
    string s2;
    s2.resize(len, '0');
    cout << "S1: " << s1 << " | Len: " << s1.size() << " | Cap: " << s1.capacity() << '\n'; // Cap: 20
    cout << "S2: " << s2 << " | Len: " << s2.size() << " | Cap: " << s2.capacity() << '\n'; // Cap: 30
}

[Mis1eader-dev]

Wait I forgot to to test it on longer payloads, may have to split this implementation into 2 functions.

[Mis1eader-dev]

Surprisingly it works for longer inputs too, I don't know how.
Welp, if it works it works. ¯\(ツ)/¯

[Mis1eader-dev]

One small thing to keep note of, in one of the inner loops where it does a copy ahead is not safe, it could read up to 3 bytes outside of the input buffer, but they will not be used after the outer loop is finished executing.
If you need me to make it tightly safe within bounds, I'll add a few checks in there to make sure it never reads outside of the initial inLen.