ggml : add GGML_OP_COL2IM_1D (#24206)

* cpu: add GGML_OP_COL2IM_1D

Add the overlap-add (scatter-add) step of a 1D transposed convolution.
A ConvTranspose1d factorizes as a GEMM followed by col2im: a weight
pre-permuted to [IC, K*OC] is contracted against the [IC, T_in] input
with mul_mat to produce a column matrix [K*OC, T_in], and col2im_1d
scatters those columns back into the [T_out, OC] signal, with
T_out = (T_in - 1)*s0 + K - 2*p0.

Keeping the contraction as a plain mul_mat leaves the heavy work on the
optimized (and quantizable) matmul kernels, so col2im_1d only does the
cheap overlap-add.

CPU uses a gather formulation parallelized over output channels,
supporting F32, F16 and BF16 with an F32 accumulator.

* tests: add backend coverage for GGML_OP_COL2IM_1D

Add test_col2im_1d next to the conv_transpose_1d cases, covering F32,
F16 and BF16 across eight geometries: the canonical kernel = 2*stride
DAC upsampling shape, overlap, no overlap, cropping (p0 = 1 and
p0 = stride/2), kernel < stride with zeroed gaps, kernel not a
multiple of stride, and a single column unfold.

Perf mode gets three real vocoder stage shapes reporting memory
bandwidth. max_nmse_err relaxes to 5e-4 for F16 and BF16.

* cpu: harden GGML_OP_COL2IM_1D

ggml_col2im_1d validates s0, oc, p0 and input contiguity at graph
build time, before the oc division, protecting every backend at once.
The kernel asserts the contiguity its flat indexing assumes and its
doc states the full output length including the crop term.

The kernel parallelizes over the time axis: the split stays balanced
down to OC = 1, where the previous channel split was single threaded.
Values are bit identical on the three real vocoder chains, two out of
three improve.

* tests: extend the GGML_OP_COL2IM_1D grid

The eval grid grows to eleven geometries: OC = 1 (mono output stage),
K = 1 with stride > 1 (sparse scatter, every gap position zeroed) and
a crop down to T_out = 2 where all the gather bounds act at once.

* tests: add col2im_1d equivalence test

tests/test-col2im-1d.cpp proves mul_mat + col2im_1d matches the
native ggml_conv_transpose_1d on the CPU backend, F32 bit exact, F16
and BF16 through casts of the column matrix. test-backend-ops cannot
cover this for a CPU only op since the CPU backend is its own
reference there.

* rpc: bump protocol patch version for GGML_OP_COL2IM_1D

GGML_OP_COUNT goes from 96 to 97 with the new op, which trips the
static_assert in ggml-rpc.h. Bump RPC_PROTO_PATCH_VERSION since the
op is appended and no existing op code shifts.

ggml/src/ggml-cpu/ops.cpp

@@ -6730,6 +6730,78 @@ static inline int64_t ggml_wrap_around(int64_t coord, int64_t size) {
     return (coord  + size) % size; // adding size avoids negative number weirdness
 }
 
+// ggml_compute_forward_col2im_1d
+//
+// Scatter-add columns [K*OC, T_in] -> signal [T_out, OC]
+// where T_out = (T_in - 1)*s + K - 2*p.  Gather approach: each output reads ceil(K/s) inputs.
+// Parallelized over the time axis so the split stays balanced whatever OC is.
+// Supports F32, F16, BF16 input/output (same type), F32 accumulator.
+
+template <typename elem_t>
+static void ggml_compute_forward_col2im_1d_impl(
+        const ggml_compute_params * params,
+        ggml_tensor * dst) {
+
+    const ggml_tensor * src = dst->src[0];  // [K*OC, T_in]
+
+    GGML_ASSERT(ggml_is_contiguous(src));
+    GGML_ASSERT(ggml_is_contiguous(dst));
+
+    const int32_t s0 = ((const int32_t *)(dst->op_params))[0];
+    const int32_t OC = ((const int32_t *)(dst->op_params))[1];
+    const int32_t p0 = ((const int32_t *)(dst->op_params))[2];
+
+    const int64_t K_OC = src->ne[0];
+    const int64_t T_in = src->ne[1];
+    const int64_t K    = K_OC / OC;
+    const int64_t T_out = dst->ne[0];
+
+    const elem_t * col_data = (const elem_t *) src->data;
+    elem_t       * dst_data = (elem_t *) dst->data;
+
+    const int ith = params->ith;
+    const int nth = params->nth;
+
+    // Parallelize over the time axis: the split stays balanced whatever OC is,
+    // down to OC = 1 for mono audio, and threads read disjoint column bands
+    const int64_t dr = (T_out + nth - 1) / nth;
+    const int64_t it0 = dr * ith;
+    const int64_t it1 = it0 + dr < T_out ? it0 + dr : T_out;
+
+    for (int64_t oc = 0; oc < OC; oc++) {
+        for (int64_t t_out = it0; t_out < it1; t_out++) {
+            const int64_t t_abs = t_out + p0;  // absolute position in uncropped signal
+            // Gather: find all (t_in, k) where t_in * s + k == t_abs, 0 <= k < K
+            int64_t t_in_min = (t_abs - K + 1 + s0 - 1) / s0;  // ceil((t_abs-K+1)/s)
+            if (t_in_min < 0) t_in_min = 0;
+            int64_t t_in_max = t_abs / s0;
+            if (t_in_max >= T_in) t_in_max = T_in - 1;
+
+            float sum = 0.0f;
+            for (int64_t t_in = t_in_min; t_in <= t_in_max; t_in++) {
+                int64_t k = t_abs - t_in * s0;
+                if (k >= 0 && k < K) {
+                    // col layout: [K*OC, T_in], element (oc*K+k, t_in)
+                    sum += type_conversion_table<elem_t>::to_f32(col_data[(oc * K + k) + t_in * K_OC]);
+                }
+            }
+            // dst layout: [T_out, OC], element (t_out, oc)
+            dst_data[t_out + oc * T_out] = type_conversion_table<elem_t>::from_f32(sum);
+        }
+    }
+}
+
+void ggml_compute_forward_col2im_1d(
+        const ggml_compute_params * params,
+        ggml_tensor * dst) {
+    switch (dst->src[0]->type) {
+        case GGML_TYPE_F32:  ggml_compute_forward_col2im_1d_impl<float>      (params, dst); break;
+        case GGML_TYPE_F16:  ggml_compute_forward_col2im_1d_impl<ggml_fp16_t>(params, dst); break;
+        case GGML_TYPE_BF16: ggml_compute_forward_col2im_1d_impl<ggml_bf16_t>(params, dst); break;
+        default: GGML_ABORT("col2im_1d: unsupported type %d", dst->src[0]->type);
+    }
+}
+
 // ggml_compute_forward_conv_2d