Pass arguments by const reference to avoid making copies

[jmcarcell]

BEGINRELEASENOTES

• Pass arguments by const reference to avoid making copies in a few places where passing by value was used

ENDRELEASENOTES

I think copies are not needed in these places

[tmadlener]

I am not particularly liking this because it's a bit misleading, because something down the line will be stealing the data from these buffers:

podio/python/templates/CollectionData.cc.jinja2

Lines 35 to 36 in 53ded81

	m_refCollections(std::move(*buffers.references)),
	m_vecmem_info(std::move(*buffers.vectorMembers)) {

On the other hand this is the case already now because the copy we make at the moment will also have the same behavior. In the end all of this should be cleaned up better at some point (see #506).

Interestingly this also seems to work even though we technically assign to a different std::function:

podio/include/podio/CollectionBuffers.h

Line 51 in 53ded81

using CreateFuncT = std::function<std::unique_ptr<podio::CollectionBase>(podio::CollectionReadBuffers, bool)>;