Clamp the patch merge to ±2π in the native Swin encoders

NVIDIA's enc1 and enc2 clamp the patch merge's result to ±2π (as f16) before
its e4m3 encoding (max.f16x2 / min.f16x2 with 0fC0C90FDB / 0f40C90FDB after the
merge's last MMA). The native layers did not, in either template or set:
merge_clamp (swin_common.h) now does, at the three sites that encode the merged
tokens (swin_block.h's e4m3-activation and f16 paths, swin_tok.h), and
swin_check.py's model clamps the same way.

Measured on an RX 9070 XT against a run with no native kernels (preset L,
accuracy set, the flags of Ghost of Tsushima, 1280x720 -> 3840x2160, one
frame): native enc1 alone 34 dB and enc2 alone 31 dB from the translated
kernels before, byte-identical after; the whole native set 28 -> 80 dB (the
rest is dec1, 0.09% of the output values). Preset M's fast set against
translated M: 30.8 -> 35.1 dB after 30 frames. The gfx11 path has the same
change and was not run on hardware.

The repo's tests pass (36, 3 skipped).

kernels/m/swin_tok.h

@@ -738,7 +738,8 @@ __device__ __forceinline__ void swin_tok_block(const CommonParams& p, const Tube
 #pragma unroll
                     for (int kc = 0; kc < C / 8; ++kc)
                         k32(y, wt(K::PM, NTP, kc, 0, u), as[kc][0], wt(K::PM, NTP, kc, 1, u), as[kc][1]);
-                    const u2v code = tok_codes(y);
+                    const u2v code = {codes4(merge_clamp(y.pair(0)), merge_clamp(y.pair(1))),
+                                      codes4(merge_clamp(y.pair(2)), merge_clamp(y.pair(3)))};
                     if (inside)
                         *(u2v*)(p.p48 + ((size_t)((u >> 1) * H2 + MY) * W2 + MX) * 32 + 16 * (u & 1) + 8 * hf) = code;
                 }