FabricSummary (v2): address tech debt (#564)

* Address FabricSummary (v2) tech debt

1. Unit tests for FabricSummary (v2)

- This class did not have unit tests, added unit tests and fixtures
- Updated dcnm_fabric/utils.py with FabricSummary (v2) support

2. FabricSummary (v2)

- Added type hints throughout
- Updated docstrings to use Markdown throughout
- Made several public instances private (e.g. self.conversion -> self._conversion)
- Updated rest_send and results properties with enhanced versions we use in other classes

* Appease linters

No functional changes in this commit

* Use private attributes instead of property getters when calculating device count.

Use private attributes instead of property getters when calculating device count. The current code calls property getters (self.leaf_count, self.spine_count, self.border_gateway_count) which invoke verify_refresh_has_been_called(), adding unnecessary overhead.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* FabricSummary (v2): Explain why lines are commented

No functional changes in this commit.

Addressing a Copilot comment regarding commented lines in fabric_summary_v2.py

* Remove redundant empty data check in all_data property.

Address below Copilot review comment.

[nitpick] Remove redundant empty data check in all_data property. After a successful call to refresh(), self.data cannot be empty ({}) because _verify_controller_response() at line 212 would have raised a ControllerResponseError. The verify_refresh_has_been_called() call at line 318 already ensures refresh() completed successfully. This additional check is unnecessary and inconsistent with other properties like border_gateway_count, device_count, etc.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Remove rest_send getter validation

Addressing the below Copilot review comment.

[nitpick] The rest_send property getter validation prevents accessing the property before calling the setter, which is overly restrictive. Internal methods like _set_fabric_summary_endpoint() (line 176) use self.rest_send.path, which would fail this check. While refresh() validates params at line 245 before calling _set_fabric_summary_endpoint(), this getter-level validation adds unnecessary coupling and prevents legitimate use cases like inspecting the rest_send object. Consider removing lines 457-460 from the getter, as the setter and refresh() method already provide adequate validation.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: allenrobel