feat(component-failover-adoption): unify worker's dual connect paths into single pipeline

Replace worker's separate default/single-host and multi-candidate connect
branches with one path: synthesize-or-accept a candidate list, validate,
convert via xce_cluster_config_to_client_config(), connect once. Register
a flag-only rejoin callback (no I/O, no client-lib reentry) and remove the
liveness probe's bounded give-up so the library owns retry/recovery.

src/worker/meson.build

@@ -103,3 +103,5 @@ xcecd_virtual = executable('xcecd_virtual',
                            include_directories: [incdir],
                            dependencies:[xcecd_deps],
                            install:true)
+
+subdir('testsuite')