Fix Python 3.12 incompatibility in versioneer.py

[rbaiazitovRBNT]

Summary

pkasolver fails to install or build on Python 3.12+ because versioneer.py uses two APIs that were removed in Python 3.12 (both had been deprecated since Python 3.2):

Removed API	Replacement
configparser.SafeConfigParser()	configparser.RawConfigParser()
parser.readfp(f)	parser.read_file(f)

The errors at build time are:

AttributeError: module 'configparser' has no attribute 'SafeConfigParser'
AttributeError: 'RawConfigParser' object has no attribute 'readfp'

What changed

One file, two one-line substitutions in versioneer.py:

-    parser = configparser.SafeConfigParser()
+    parser = configparser.RawConfigParser()
     with open(setup_cfg, "r") as f:
-        parser.readfp(f)
+        parser.read_file(f)

Both replacements are fully API-compatible and have been available since Python 3.2, so this patch does not affect older Python versions.

Why it matters

Python 3.12 is now the default on many platforms (macOS Homebrew, recent Ubuntu, etc.). Without this fix, users on Python 3.12 cannot pip install pkasolver at all — the build step errors out before any package code runs. This is a one-line versioneer maintenance fix with zero functional impact on the library itself.

Test plan

• pip install . succeeds on Python 3.12
• import pkasolver works after install
• pKa predictions return expected values (tested against literature values for common aliphatic amines)