Tests: Refactors lease dedup tests to eliminate duplication

Consolidates 8 separate test methods into parameterized tests + shared helpers:
- 4 PK behavior tests -> 1 DataTestMethod with 4 DataRows (PKRange/EPK x default/opt-out)
- 2 dedup 409 tests -> 1 DataTestMethod with 2 DataRows (PKRange/EPK)
- 2 back-compat tests share CreatePreExistingGuidPkLease helper

New helpers: CreatePkCapturingMockContainer, CreateDedupSimulatingMockContainer,
CreateLeaseManager, CreateLeaseAsync, CreatePreExistingGuidPkLease.

Net reduction: ~160 lines removed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: kirankumarkolli