[C++] Add support for nested class types in row encoder

[PragmaTwice]

What do these changes do?

Nested struct/class types is finally supported! e.g

struct A { ... };
FURY_FIELD_INFO(A, ...);

struct B { ... };
FURY_FIELD_INFO(B, ...);

struct D {
  int x;
  A y;
  B z;
};
FURY_FIELD_INFO(D, x, y, z);

RowWriter writer(encoder::RowEncodeTrait<D>::Schema());
writer.Reset();

D d{233, {234, 3.14, true}, {235, "hi"}};
encoder::RowEncodeTrait<D>::Write(d, writer);
...

Check code requirements

• tests added / passed (if needed)
• Ensure all linting tests pass, see here for how to run them

[chaokunyang]

LGTM, now fury cpp is much more feature completed