Return void from McpStatelessSyncServer#closeGracefully instead of Mo… #503

Job	Run time
Server Conformance	56s
Client Conformance (initialize)	43s
Client Conformance (sse-retry)	45s
Client Conformance (tools_call)	56s
Client Conformance (elicitation-sep1034-client-defaults)	42s
Auth Conformance (auth/metadata-var1)	44s
Auth Conformance (auth/basic-cimd)	49s
Auth Conformance (auth/scope-from-www-authenticate)	45s
Auth Conformance (auth/scope-retry-limit)	51s
Auth Conformance (auth/metadata-default)	48s
Auth Conformance (auth/metadata-var3)	53s
Auth Conformance (auth/metadata-var2)	50s
Auth Conformance (auth/scope-step-up)	1m 5s
Auth Conformance (auth/scope-omitted-when-undefined)	40s
Auth Conformance (auth/token-endpoint-auth-none)	50s
Auth Conformance (auth/token-endpoint-auth-post)	58s
Auth Conformance (auth/token-endpoint-auth-basic)	56s
Auth Conformance (auth/pre-registration)	47s
Auth Conformance (auth/scope-from-scopes-supported)	53s
	15m 51s

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