build(deps): bump pnnx from 20250930 to 20251031 in /requirements

Bumps [pnnx](https://github.com/Tencent/ncnn) from 20250930 to 20251031.
- [Release notes](https://github.com/Tencent/ncnn/releases)
- [Commits](https://github.com/Tencent/ncnn/commits)

---
updated-dependencies:
- dependency-name: pnnx
  dependency-version: '20251031'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/inference.txt

@@ -1,5 +1,5 @@
 libusb1>=3.0.0
-pnnx==20250930
+pnnx==20251031
 ncnn>=1.0.20230517
 onnx>=1.14.0
 onnxmltools>=1.11.2