fix(sitemanage): clear test-source Xlint residual (#3159)

[natechadwick-intsof]

Summary

Clears all 60 projects/sitemanage test-source project -Xlint diagnostics after main-source misc residual (#3107 / open PR #3158). Real fixes preferred; main sources untouched.

Clusters

Cluster	Approach
this-escape REST clients	Final/safe helpers; protected requestHeaders/postContentType seeds; PSRestClient(String) ctor chain; no redundant fillInStackTrace
serialVersionUID	Nested concurrency/exception stubs + dummy validation exceptions
serial-field	transient parsed error payloads on REST client exceptions
unchecked	TypeReference JSON; typed ArgumentCaptor; chained thenReturn; typed dao mock
heap-pollution	@SafeVarargs on PSTestDataCleaner
sun.misc.Unsafe	Real constructors / Mockito shells for path-injection tests (security asserts preserved)
static	PSThumbnailProcessMonitor.* qualified by type name

Inventory

Metric	Before	After
test-source Xlint	60	0

Test plan

• cd projects/sitemanage && ../../mvnw.cmd clean install — BUILD SUCCESS
• Tests run: 1090, Failures: 0, Errors: 0, Skipped: 125
• test-compile -Dmaven.compiler.showWarnings=true — test-source [WARNING] *.java: 0
• Path-injection suites still reject traversal/NUL/separator payloads
• C2: no production final/signature changes — N/A

Product documentation

• N/A — pure compiler lint tech debt; no operator/user/API surface change

Gates / evidence (C3)

• modules_built: projects/sitemanage
• build_evidence: cd projects/sitemanage && ../../mvnw.cmd clean install → BUILD SUCCESS; Tests run: 1090, Failures: 0, Errors: 0, Skipped: 125; test-source Xlint 60→0
• downstream_checked: none (C2 did not apply — test-source only; no production final/signature/package API shape changes)
• C5 UI: N/A — no UI surface

Operator

Operator: Grok: night-issue-prs (model grok-4.5)

Parent: #2032 / #2200
Fixes #3159 (sitemanage test-source Xlint residual after #3107).

Co-Authored by Grok Build using grok-4.5 with agent main.