add install_torch_sitrep(), a Situation Report for torch install.

[cregouby]

Fix #1411
Provide a situation report for torch installation

── System Information ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
• OS: "Darwin" (26.0)
• R Version: "R version 4.5.2 (2025-10-31)"
• Platform: "aarch64-apple-darwin20"
• Architecture: "arm64"

── Package Information ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
• torch package: "0.16.3.9000"
• LibTorch: "unknown"

── Installation Status ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
ℹ Installation path: ~/R/torch/inst
✔ Torch installation files found
✔ Lantern library found
✔ LibTorch libraries found
Library files:
• libc10.dylib
• liblantern.dylib
• libtorch_cpu.dylib
• libtorch_global_deps.dylib
• libtorch.dylib

── Lantern Loading Status ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
✔ Lantern is loaded and initialized

── Library Dependencies ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
✔ Library dependency check available via otool
Dependencies for liblantern.dylib:
~/R/torch/inst/lib/liblantern.dylib:
@rpath/liblantern.dylib (compatibility version 0.0.0, current version 0.0.0)
@rpath/libc10.dylib (compatibility version 0.0.0, current version 0.0.0)
@rpath/libtorch.dylib (compatibility version 0.0.0, current version 0.0.0)
@rpath/libtorch_cpu.dylib (compatibility version 0.0.0, current version 0.0.0)
/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1300.23.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1311.100.3)

── CUDA Status ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
ℹ Installation type: "cpu"
✖ CUDA is NOT available (or Lantern not loaded)

── Backend Status ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
✖ cuDNN is NOT available
✖ MKL is NOT available
✖ MKL-DNN is NOT available
✖ OpenMP is NOT available
✔ MPS (Apple Silicon GPU) is available

── Environment Variables ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
ℹ No torch-related environment variables set

── Issues and Recommendations ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────
✔ No issues detected

(written with the help of GLM and Claude Sonnet)