Move bitflip utils function to aidge_core

Context

The bitflip functions used in fault injection nodes were previously duplicated across cpu kernels (not merged yet, see aidge_backend_cpu!188 (merged))

Move them all in aidge_core to reduce code duplication.

Detailed major modifications

• Add utility function to flip a single bit for types of size 1,4 and 8 bytes in aidge_core.
• Add the associated tests