fix(core): receive path — replay window covers the loss window, zero-alloc open

Two receive-path findings from the networking audit:

1. The anti-replay window (4096 seqs) silently re-tightened the "late ≠ lost"
   fix: at 1 Gbps (~125k pkt/s) it spans only ~33 ms, so a Wi-Fi-retry-delayed
   shard the reassembler's 120 ms loss window would still use was dropped HERE
   first as "older than the window" — recreating the false-loss → recovery-IDR
   churn the time-based loss window was built to kill, exactly on the high-rate
   links punktfunk targets. Widened to 32768 (covers 120 ms up to ~270k pkt/s,
   ≈2 Gbps+); the bitmap costs 4 KiB per session and the replay-hiding bound
   stays finite.

2. Every received datagram still paid one Vec allocation in the AES-GCM open
   (and a to_vec on the plaintext probe path) — ~125k allocs/s of cross-thread
   allocator churn at line rate, the same class of overhead that was the
   documented single-core wall on the macOS receive path. New
   `SessionCrypto::open_in_place` (mirror of seal_in_place; GCM verifies the
   tag BEFORE decrypting, so a forged packet never yields plaintext) lets
   `poll_frame` decrypt inside the recv ring and hand the reassembler a slice.
   Byte-identical semantics, unit-tested against `open` incl. tamper/runt
   cases; criterion entry added next to seal_in_place.

Tests: 94 core unit + loopback/c_abi suites green; clippy clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/punktfunk-core/benches/pipeline.rs

@@ -71,6 +71,15 @@ fn bench_crypto(c: &mut Criterion) {
     g.bench_function("open", |b| {
         b.iter(|| black_box(client.open(0, black_box(&sealed)).unwrap()))
     });
+    g.bench_function("open_in_place", |b| {
+        // In-place open consumes the buffer, so each iteration restores the ciphertext first —
+        // one memcpy, mirroring what the recv ring does when the next datagram lands in the slot.
+        let mut buf = sealed.clone();
+        b.iter(|| {
+            buf.copy_from_slice(black_box(&sealed));
+            black_box(client.open_in_place(0, &mut buf).unwrap());
+        })
+    });
     g.finish();
 }