ENH: Update pyproject.toml for ITK 5.4.2

In preparation for release.

Ensure that cmake is 3.16.3 or greater to
match v5.4.2 minimum requirements.

Set minimum python to 3.9

Increment version number.

Replace keyword of "ITK" with lowercase "itk"
in some instances to be consistent.

Author: hjmjohnson

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "scikit_build_core.build"
 
 [project]
 name = "itk-bsplinegradient"
-version = "1.0.0"
+version = "1.0.1"
 description = "Approximate an image's gradient from a B-spline fit to its intensity."
 readme = "README.rst"
 license = {file = "LICENSE"}
@@ -36,7 +36,7 @@ classifiers = [
     "Topic :: Scientific/Engineering :: Medical Science Apps.",
     "Topic :: Software Development :: Libraries",
 ]
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 dependencies = [
     "itk == 5.4.*",
     "itk-meshtopolydata == 0.12.*",