Documentation Updates for cuML Python Developer Guide (#6843)

This PR addresses several documentation improvements outlined in the issue, focusing on the Python Developer Guide and Estimator Guide.

### Core Documentation Updates
- Completed logging section with usage guidance, best practices and examples
- Completed "Device and Host Memory" section with RMM integration details
- Completed "Multi GPU" section with usage patterns and limitations
- Expanded API documentation guidelines with docstring formatting standards and examples
- Improved section order and overall flow

### Estimator Guide Revisions
- Updated guide to clarify API matching policy:
  - Match scikit-learn/umap-learn APIs where possible and reasonable
  - API deviations must be well-justified and documented
  - Unused parameters or arguments should generally not be matched
  - Exact API matching is not required; consumers should use cuml.accel if that is needed

- Content Organization:
  - Deleted all sections referencing cuml-cpu functionality
  - Added explicit requirement for keyword-only arguments in constructors

### Memory Management Terminology
- Revised documentation to use "accessibility" terminology instead of physical location references
- Updated memory management sections to acknowledge that memory can be host or device accessible
- Removed references to cuml-cpu related components

Closes #6850 .

Authors:
  - Simon Adorf (https://github.com/csadorf)

Approvers:
  - Jim Crist-Harif (https://github.com/jcrist)

URL: #6843

Author: csadorf