Gate native RDMA, cuObject, and cuobjclient implementations behind the
rdma build tag while keeping fallback stubs available for standard builds.
Preserve the separate cuobjclient_host configuration, clarify unsupported
platform errors, and update Makefile RDMA targets to pass the required tags
and disable VCS stamping.
Co-authored-by: Ben McClelland <ben.mcclelland@versity.com>
Add a SessionsSnapshot view over the new C ABI entry point and
serve it from the admin server as GET /rc-sessions. The admin server
gains a WithAdminRoute option so an embedding binary can register
extra admin routes that run with the same signature verification and
admin checks as the built-in endpoints; vgwrdma registers the
snapshot there when the RC feature is enabled. The route replies
with the usual XML error surface so unsigned or non-admin requests
get a 403 rather than a generic 500. Stub builds return a not
supported error, keeping the build matrix unchanged.