Update: Require Python 3.9+, upgrade dependencies for security fixes

- Changed minimum Python version from 3.8 to 3.9
- Added Python 3.13 and 3.14 classifiers
- Updated ruff target-version to py39
- Upgraded dependencies with security fixes:
  - urllib3: 2.6.3 (CVE fix)
  - setuptools: 80.9.0 (CVE fix)
  - pymdown-extensions: 10.20 (CVE fix)

Co-Authored-By: Amp <amp@ampcode.com>

Author: heikkitoivonen

pyproject.toml

@@ -7,7 +7,7 @@ license = { text = "MIT" }
 authors = [
     { name = "Python Complexity Contributors" }
 ]
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 keywords = [
     "complexity",
     "time-complexity",
@@ -21,11 +21,12 @@ classifiers = [
     "License :: OSI Approved :: MIT License",
     "Operating System :: OS Independent",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.8",
     "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 :: 3.14",
     "Topic :: Education",
     "Topic :: Software Development",
 ]
@@ -59,7 +60,7 @@ dev = [
 ]
 
 [tool.ruff]
-target-version = "py38"
+target-version = "py39"
 line-length = 100
 exclude = [
     ".git",