Fix all instances of W605 (invalid escape sequence)

bilby/core/result.py

bilby/gw/likelihood/base.py

bilby/gw/likelihood/multiband.py

bilby/gw/prior.py

bilby/gw/result.py

examples/core_examples/hyper_parameter_example.py

examples/core_examples/slabspike_example.py

setup.cfg

test/core/prior/base_test.py

test/core/prior/dict_test.py