chore: vendor selva_core from jnwnlee/selva@d7d40a9

Pure PyTorch SelVA source for SelvaModelLoader/FeatureExtractor/Sampler nodes.
Imports rewritten from selva.* to selva_core.*. mel_converter.py: replaced
librosa.filters.mel with pure-numpy implementation to avoid librosa→numba→NumPy
version incompatibility in some ComfyUI environments.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

selva_core/utils/transforms.py

@@ -0,0 +1,20 @@
+import torch
+
+
+def generate_multiple_segments(
+        x: torch.Tensor,
+        segment_size: int,
+        step_size: int,
+    ) -> torch.Tensor:
+        # x: (B, T, ...)
+        b, t, *rest = x.shape
+        assert t >= segment_size, f'The length of the input tensor {t} is less than the segment size {segment_size}.'
+        assert segment_size > step_size, f'The segment size {segment_size} should be greater than the step size {step_size}.'
+        # partition the tensor into segments
+        num_segments = (t - segment_size) // step_size + 1
+        segments = []
+        for i in range(num_segments):
+            segments.append(x[:, i * step_size:i * step_size + segment_size])
+        x = torch.stack(segments, dim=1)
+        
+        return x  # (B, S, T, ...)