packaging: replace deprecated setup.cfg with pyproject.toml

Update to the modern practice of a using a single declarative
pyproject.toml file for package configuration.

`setup.cfg` is deprecated and is no longer necessary.

Ref: pypa/setuptools#3214

CHANGES.rst

@@ -1,3 +1,8 @@
+Upcoming
+========
+    * The ``setup.cfg`` packaging configuration has been replaced by
+      ``pyproject.toml``. (+527)
+
 v3.3.0
 ======
     * The unpickler was updated to avoid using ``eval``, which helps improve its

pyproject.toml

@@ -1,7 +1,82 @@
 [build-system]
-requires = ["setuptools>=56", "setuptools_scm[toml]>=3.4.1"]
+requires = ["setuptools>=61.2", "setuptools_scm[toml]>=6.0"]
 build-backend = "setuptools.build_meta"
 
+[project]
+name = "jsonpickle"
+authors = [
+    { name = "Theelx" },
+    { name = "David Aguilar", email = "[email protected]" },
+]
+description = "jsonpickle encodes/decodes any Python object to/from JSON"
+classifiers = [
+    "Development Status :: 5 - Production/Stable",
+    "Intended Audience :: Developers",
+    "License :: OSI Approved :: BSD License",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3 :: Only",
+]
+requires-python = ">=3.7"
+dependencies = [
+]
+dynamic = ["version"]
+
+[project.readme]
+file = "README.rst"
+content-type = "text/x-rst"
+
+[project.urls]
+Documentation = "https://jsonpickle.readthedocs.io/"
+Homepage = "https://jsonpickle.readthedocs.io/"
+Source = "https://github.com/jsonpickle/jsonpickle"
+
+[project.optional-dependencies]
+dev = [
+    "black",
+]
+testing = [
+    # core
+    "pytest >= 6.0, != 8.1.*",
+    "pytest-benchmark",
+    "pytest-benchmark[histogram]",
+    "pytest-checkdocs >= 1.2.3",
+    "pytest-enabler >= 1.0.1",
+    "pytest-ruff >= 0.2.1",
+    # local
+    "bson",
+    "ecdsa",
+    "feedparser",
+    "gmpy2",
+    "numpy",
+    "pandas",
+    "pymongo",
+    "scikit-learn",
+    "scipy>=1.9.3; python_version > '3.10'",
+    "scipy; python_version <= '3.10'",
+    "simplejson",
+    "sqlalchemy",
+    "ujson",
+]
+docs = [
+    "furo",
+    "rst.linker >= 1.9",
+    "sphinx >= 3.5",
+]
+packaging = [
+    "build",
+    "setuptools>=61.2",
+    "setuptools_scm[toml]>=6.0",
+    "twine",
+]
+
+[tool.setuptools]
+packages = [
+    "jsonpickle",
+    "jsonpickle.ext",
+]
+include-package-data = true
+license-files = ["LICENSE"]
+
 [tool.black]
 skip-string-normalization = true