Move `experimental.algebra` to `cuqi.algebra`

[amal-ghamdi]

General description of task

Move experimental.algebra to cuqi.algebra

Definition of Done (Feature/change)

• Move experimental.algebra to cuqi.algebra and make any needed updates

Definition of Done (Mandatory)

• (N/A) Documentation added (docstrings on all public methods/classes)
• (N/A) Unit tests added/updated (and passing!)
• Code reviewed and approved by 2 CUQI-maintainers
• (N/A) Online documentation is rendered correctly (esp. math)

Definition of Done (Optional)

• (N/A) HowTo/tutorial added

[jakobsj]

DoD approved.