spectral: vectors instead of new[]; vlaw: extract law + vlaw_check target

- spectral.cpp: window_/buf_/tmp_buf_/fir_buf_/fir_freq_ as std::vector (no
  exception-leak in ctor, destructor = default)
- framed_model.hpp: extract vlaw_cut/vlaw_mask inline (BLOCKMAP:314 softplus)
- dsp/vlaw_check.cpp: unit test for law (monotonic, zero-level, delta, ref,
  comb-neutral) — PASS
- CMake: add vlaw_check target
- Guard: corpus --compare d=+0.000, fn529fe0_check PASS, twin_check PASS

dsp/spectral.hpp

@@ -21,12 +21,12 @@ public:
 private:
     size_t nfft_;
     size_t hop_;
-    double* window_;
+    std::vector<double> window_;
     FFTPlan plan_;
-    std::complex<double>* buf_;
-    std::complex<double>* tmp_buf_;
-    std::complex<double>* fir_buf_;
-    std::complex<double>* fir_freq_;
+    std::vector<std::complex<double>> buf_;
+    std::vector<std::complex<double>> tmp_buf_;
+    std::vector<std::complex<double>> fir_buf_;
+    std::vector<std::complex<double>> fir_freq_;
     std::vector<double> fir_window_;
     std::vector<float> overlap_;
     std::vector<float> mask_;