Fixes # seg-res-net refactor

Description

Refactored SegResNet forward method to separate encoder and decoder stacks to make it easier to implement the encoder in other architectures

Status

Work in progress

Types of changes

• [] Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.