[Enhance]: Transformation speed

[LElgueddari]

Is your feature request related to a problem? Please describe.
For Wavelets with pywt backend, the complex numbers are supported while the current implementation is performing twice the same decomposition (real and imag part) this could be removed for pywt backend making the transforms twice faster

Describe the solution you'd like
Checking the backend of the transforms and to leave complex value numbers for ISAP transforms

This holds for both analysis and synthesis

Are you planning to submit a Pull Request?

• Yes
• No