Add equivalent circuit models

[BradyPlanden]

Feature description

Extend PyBOP's available models by adding PyBaMM's thevenin() model class.

Motivation

No response

Possible implementation

Compose pybamm.thevenin() into pybop.ecm (or similar) following the single particles model template:

PyBOP/pybop/models/lithium_ion/base_echem.py

Line 5 in a66be81

class SPM(BaseModel):

To do:

1. Build requirements
2. Standarised options
3. Documentation
4. Examples
5. Tests

Additional context

No response