build: define trove classifiers in pyproject.toml

Move the classifiers into [project].classifiers so they ship in the
published package metadata, and drop the unused classifiers.txt.

Closes #21

Author: hartym

CHANGELOG.rst

@@ -19,5 +19,11 @@ Added
 Changed
 -------
 
-- Synced the supported Python versions in ``classifiers.txt`` and
-  ``docs/release.rst`` to list 3.10 to 3.14.
+- Moved the package trove classifiers into ``pyproject.toml`` so they ship in
+  the published metadata, covering Python 3.10 to 3.14.
+- Updated the supported Python version range in ``docs/release.rst``.
+
+Removed
+-------
+
+- ``classifiers.txt``, which was not read by the build.

pyproject.toml

@@ -12,6 +12,22 @@ authors = [
 readme = "README.rst"
 license = {file = "LICENSE"}
 requires-python = ">=3.10"
+classifiers = [
+    "Development Status :: 5 - Production/Stable",
+    "Intended Audience :: Developers",
+    "Intended Audience :: Information Technology",
+    "License :: OSI Approved :: Apache Software License",
+    "Programming Language :: Python",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3 :: Only",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
+    "Programming Language :: Python :: 3.14",
+    "Topic :: Software Development :: Libraries",
+    "Topic :: Utilities",
+]
 dependencies = []
 
 [dependency-groups]