[Store][MasterService Tests] Migrate placement, replication, and task RPC scenarios

Parent: #3098\nDepends on: #3572\n\nMigrate client-visible placement and replication behavior after the object lifecycle stack layer.\n\nScope:\n- placement and allocation responses;\n- copy, move, replication, and replica clearing;\n- task creation, fetching, completion, and query behavior;\n- segment lifecycle and client networking queries that belong to this control-plane slice.\n\nPrivate refcount, allocator, worker, and RPC-adapter invariants remain focused direct tests.

Read dependency #3572 and the parent issue #3098 first to understand the object lifecycle stack and migration boundaries. Identify the existing MasterService test scenarios for placement, replication, tasks, segments, and client networking, then migrate those listed behaviors while keeping private refcount, allocator, worker, and RPC-adapter invariants as direct tests.

Written by the indexing model from the issue text.