refactor: fix mutable default arguments in backend __init__ methods (#3354)

Replace mutable default arguments (e.g., `options=SomeOptions()`) with
`None` and initialize inside functions to prevent shared state issues.
Affects 15 backend classes across the codebase.

Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>
Co-authored-by: Panos Vagenas <pva@zurich.ibm.com>