fix(test): drop stale fixture root imports in application tests

Restoring the shared fixture root helper (bcde960) fixed
work_placement_service but left multi_root_scope_set and
workflow_fan_out_census importing a helper they never call, failing the
blocking clippy policy (-D unused-imports) on this branch.

Co-authored-by: Zack Jackson <ScriptedAlchemy@users.noreply.github.com>

Author: cursoragent

crates/tracedecay-application/tests/multi_root_scope_set.rs

@@ -3,7 +3,6 @@ mod common;
 use std::collections::BTreeSet;
 use std::fmt;
 
-use common::fixture_abs_root;
 use serde_json::json;
 use tracedecay_application::{
     AuthorizedRootAdmission, AuthorizedScopeSet, AuthorizedScopeSetAuthority, CancellationContext,

crates/tracedecay-application/tests/workflow_fan_out_census.rs

@@ -2,7 +2,6 @@ mod common;
 
 use std::collections::{BTreeMap, BTreeSet};
 
-use common::fixture_abs_root;
 use tracedecay_application::{
     CancellationContext, WorkflowFailurePolicy, WorkflowFanOutCensusEvidenceV1,
     WorkflowFanOutRequest, WorkflowProviderAdmission, derive_workflow_fan_out_census,