Fix pyproject.toml for modern packaging standards

- Use SPDX license expression (license = 'MIT') instead of deprecated classifier
- Remove deprecated tool.setuptools.license-files in favor of auto-detection
- Bump setuptools requirement to >=77.0.0 for SPDX support
- Add Python 3.13 classifier
- Fix MANIFEST.in: include LICENSE, exclude *.pyc/*.pyo/*.so/__pycache__
- Add check-manifest config to ignore uv.lock
- Verified: twine check passes, check-manifest passes,
  wheel and sdist both install and work correctly

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mrecachinas

MANIFEST.in

@@ -1,5 +1,11 @@
 include README.rst
+include LICENSE
 include pyproject.toml
 
 graft test
-graft src
+graft src
+
+global-exclude *.pyc
+global-exclude *.pyo
+global-exclude *.so
+global-exclude __pycache__

pyproject.toml

@@ -1,18 +1,18 @@
 [build-system]
-requires = ["setuptools>=61.0", "wheel"]
+requires = ["setuptools>=77.0.0", "wheel"]
 build-backend = "setuptools.build_meta"
 
 [project]
 name = "hexhamming"
 version = "2.2.3"
 description = "Fast Hamming distance calculation for hexadecimal strings"
 readme = "README.rst"
+license = "MIT"
 authors = [
     { name = "Michael Recachinas", email = "m.recachinas@gmail.com" }
 ]
 keywords = ["hamming", "distance", "simd"]
 classifiers = [
-    "License :: OSI Approved :: MIT License",
     "Operating System :: MacOS :: MacOS X",
     "Operating System :: POSIX :: Linux",
     "Operating System :: Microsoft :: Windows",
@@ -23,6 +23,7 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
 ]
 requires-python = ">=3.8"
 
@@ -40,11 +41,13 @@ dev = [
 [tool.setuptools]
 zip-safe = false
 packages = []
-license-files = []
 
 [tool.pytest.ini_options]
 testpaths = ["test"]
 
+[tool.check-manifest]
+ignore = ["uv.lock"]
+
 [tool.ruff]
 line-length = 88
 target-version = "py38"