feat: send a User-Agent on relay WebSocket upgrades (#9246)

Relay WebSocket clients in this repo now send a `User-Agent` of the form
`<name>/<version>` on the upgrade request. The version comes from the
build.

| Client | User-Agent |
|---|---|
| `buzz-acp` | `buzz-acp/<crate version>` |
| `buzz-cli` | `buzz-cli/<crate version>` |
| `buzz-ws-client` (default) | `buzz-ws-client/<crate version>` |
| `buzz-pairing-cli` | `buzz-pairing-cli/<crate version>` |
| `buzz-audio-client` (default) | `buzz-audio-client/<crate version>` |
| mobile (relay and huddle sockets) | `Buzz-Mobile/<app version>` |

- **`buzz-ws-client`**: every connect path sends the default. A
`User-Agent` in the caller's `connect_with_headers` headers replaces it,
so other consumers can identify themselves without any new API.
`buzz-cli` uses this to send its own name.
- **`buzz-audio-client`**: keeps a `User-Agent` already on the
host-supplied request, and adds its default otherwise.
- **Mobile**: `openRelayWebSocket` sets the HTTP client's `userAgent`,
which also covers the huddle transport. Startup waits up to 500 ms for
the app version from `package_info_plus` before the app runs, so the
first socket carries it; if the lookup fails or times out, the value is
`Buzz-Mobile`.

Each client has a test asserting the header on the upgrade request.

---------

Signed-off-by: Will Pfleger <wpfleger@block.xyz>
Co-authored-by: Hayt <211b96e6a2b7f45fd4047988976c7bbbeeda0c15f3ae7b32eec20834b5a55118@buzz.block.builderlab.xyz>

scripts/run-tests.sh

@@ -113,6 +113,12 @@ run_unit_tests() {
   run_test_step "buzz-cli tests" \
     cargo test -p buzz-cli -- --nocapture
 
+  run_test_step "buzz-ws-client tests" \
+    cargo test -p buzz-ws-client -- --nocapture
+
+  run_test_step "buzz-pairing-cli tests" \
+    cargo test -p buzz-pairing-cli -- --nocapture
+
   # buzz-sdk builder/validation unit tests: pure event-builder and input
   # validation, no infra. Mirrors the nextest path in `just test-unit` — the
   # two lists must stay in step. `--lib` matches the nextest invocation and