Use const when possible

[duarm]

Thanks for working on CMC!

What is the nature of this request?

• Change in source code details (names of variables, functions, parameters, etc)

Is your feature request related to a problem? Please describe.

some functions do not modify the collection, like the _count functions, these should have the collection parameter marked as const

Describe the solution you'd like

functions like _count, _get (except for sorted lists), _index_of, _contains should have the collection marked as const

Not a breaking change as C auto casts to const