Migrate from setup.py to pyproject.toml (#1084)

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 <csmarchbanks@gmail.com>

Author: csmarchbanks

MANIFEST.in

@@ -0,0 +1,49 @@
+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "prometheus_client"
+version = "0.21.1"
+description = "Python client for the Prometheus monitoring system."
+readme = "README.md"
+license = { file = "LICENSE" }
+requires-python = ">=3.9"
+authors = [
+    { name = "The Prometheus Authors", email = "prometheus-developers@googlegroups.com" },
+]
+keywords = [
+    "prometheus",
+    "monitoring",
+    "instrumentation",
+    "client",
+]
+classifiers = [
+    "Development Status :: 4 - Beta",
+    "Intended Audience :: Developers",
+    "Intended Audience :: Information Technology",
+    "Intended Audience :: System Administrators",
+    "Programming Language :: Python",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.9",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
+    "Programming Language :: Python :: Implementation :: CPython",
+    "Programming Language :: Python :: Implementation :: PyPy",
+    "Topic :: System :: Monitoring",
+    "License :: OSI Approved :: Apache Software License",
+]
+
+[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']

pyproject.toml

@@ -34,14 +34,14 @@ deps =
     flake8-import-order==0.18.2
 skip_install = true
 commands =
-    flake8 prometheus_client/ tests/ setup.py
+    flake8 prometheus_client/ tests/
 
 [testenv:isort]
 deps =
     isort==5.10.1
 skip_install = true
 commands =
-    isort --check prometheus_client/ tests/ setup.py
+    isort --check prometheus_client/ tests/
 
 [testenv:mypy]
 deps =