push_config()/probe_config(): build/send Request{opcode:upgradeConfig}
and the direct-struct ProbeConfigTagRequest respectively, following
redirects to the primary for the former (ProbeConfigTagReply has no
redirect fields, so probe_config connects directly). Maps controller
status/reply-variant failures to typed results/errors. Tested against
a real local TLS mock controller built from the bundled schema, since
neither opcode has a live controller-side handler today (separately
documented, unrelated to this task).
Unblocked mid-task by bug-1461 (commit e53c086): controller.capnp had
a struct-name collision that miscompiled UpgradeConfigRequest.sha256/
.bytes, making this task's core request impossible to construct via
pycapnp until fixed at the schema root.
