deps: declare fbm as a runtime dependency, not a dev extra

pyproject.toml

@@ -33,6 +33,9 @@ classifiers = [
     "Topic :: Scientific/Engineering :: Mathematics",
 ]
 dependencies = [
+    # Imported at package load: powersig/util/__init__.py pulls in fbm_utils,
+    # so the torch, cupy and jax backends all need it just to import.
+    "fbm>=0.3.0",
     "numpy>=1.26.4",
     "scikit-learn>=1.3.2",
     "tqdm>=4.67.1",
@@ -46,7 +49,6 @@ cupy = ["cupy-cuda12x>=13.4.1"]
 cupy-cuda13 = ["cupy-cuda13x>=13.6.0"]
 dev = [
     "pytest>=7.0",
-    "fbm>=0.3.0",
 ]
 all = [
     "jax[cuda13]>=0.10.0",

requirements-dev.txt

@@ -5,6 +5,5 @@ matplotlib
 git+https://github.com/crispitagorico/sigkernel.git
 git+https://github.com/geekbeast/KSig.git
 git+https://github.com/FrancescoPiatti/polysigkernel.git
-fbm
 seaborn
 datasets

requirements.txt

@@ -17,6 +17,7 @@ setuptools
 aeon
 numba==0.61.2
 cupy-cuda13x>=13.6.0
+fbm
 psutil
 tqdm==4.67.1
 jax[cuda13]>=0.10.0