fix(ci): green main again — clock_sync callers, two clippy denials, an unused import

`ci.yml`'s clippy gate has been failing on main since the pre-0.16.0 sweep landed, and
because clippy stops at the first crate it can't compile, the visible error was only
ever the first of four. `ci.yml` is not tag-triggered, so v0.16.0 cut and shipped over
a red main; none of this reaches the release artifacts (the two E0308s are in a test
binary and a dev tool, and the rest are lints) but the gate has been blind since.

Fixed, in the order clippy surfaced them:

- clients/probe failed to COMPILE (E0308, x2). `810d918d` moved `clock_sync` onto the
  resumable `io::MsgReader` but only updated the client pump, leaving the probe passing
  a bare `&mut RecvStream`. The probe now wraps the control stream in a `MsgReader` at
  `open_bi` and threads that everywhere — Welcome, the --remode and --bitrate watchers,
  and the speed-test result read — which is also what the refactor was for: those reads
  sit behind timeouts and `select!`, exactly where a straddling frame would desync the
  stream for the rest of the run.

- pf-capture: `SPA_META_Cursor as u32` is a `u32 -> u32` no-op
  (`clippy::unnecessary_cast`). Line 1274 already passes the same constant uncast, so
  the type is not in question.

- pf-inject: `noop as usize` on the SIGUSR1 wake handler added in `986402f7` trips
  `clippy::function_casts_as_integer`; goes via `*const ()` as the lint asks. Same value
  in the `usize`-typed `sa_sigaction` slot.

- punktfunk-core: the `ctrl_framing` test module's `use super::*` is unused, which
  `-D warnings` promotes to an error.

Verified with CI's own commands on a Linux box (this is all Linux-gated code, so a Mac
cannot check it): `cargo clippy --workspace --all-targets --locked -- -D warnings`
finishes clean, `cargo build --workspace --locked` succeeds, and
`cargo test --workspace --locked` exits 0 with no failures — including punktfunk-core's
196-test suite, which covers the control-stream framing the probe change touches.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/pf-capture/src/linux/mod.rs

@@ -1318,8 +1318,7 @@ mod pipewire {
         // that SIGSEGVs inside the PipeWire `.process` callback (a segfault `catch_unwind` cannot
         // catch). Every offset below is validated against `region_size` with checked arithmetic,
         // mirroring the fd-length guard the main frame path already applies to xdg-desktop-portal-wlr.
-        let meta =
-            unsafe { spa::sys::spa_buffer_find_meta(spa_buf, spa::sys::SPA_META_Cursor as u32) };
+        let meta = unsafe { spa::sys::spa_buffer_find_meta(spa_buf, spa::sys::SPA_META_Cursor) };
         if meta.is_null() {
             return;
         }