Migrate from setup.py to pyproject.toml

Update the project configuration to use a pyproject.toml file instead of
setup.py. This is the preferred tool and will allow easier integration
with other tools in the future. We can also get rid of MANIFEST.in as
the cache and compiled files are automatically excluded.

Signed-off-by: Chris Marchbanks <[email protected]>

Author: csmarchbanks

MANIFEST.in

@@ -0,0 +1,49 @@
+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "prometheus_client"
+version = "0.22.0"
+description = "Python client for the Prometheus monitoring system."
+readme = "README.md"
+license = { file = "LICENSE" }
+requires-python = ">=3.9"
+authors = [
+    { name = "The Prometheus Authors", email = "[email protected]" },
+]
+keywords = [
+    "prometheus",
+    "monitoring",
+    "instrumentation",
+    "client",
+]
+classifiers = [
+    "Development Status :: 4 - Beta",
+    "Intended Audience :: Developers",
+    "Intended Audience :: Information Technology",
+    "Intended Audience :: System Administrators",
+    "License :: OSI Approved :: Apache Software License",
+    "Programming Language :: Python",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.13",
+    "Programming Language :: Python :: 3.9",
+    "Programming Language :: Python :: Implementation :: CPython",
+    "Programming Language :: Python :: Implementation :: PyPy",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Topic :: System :: Monitoring",
+]
+
+[project.optional-dependencies]
+twisted = [
+    "twisted",
+]
+
+[project.urls]
+Homepage = "https://github.com/prometheus/client_python"
+Documentation = "https://prometheus.github.io/client_python/"
+
+[tool.setuptools.package-data]
+prometheus_client = ['py.typed']