Add cupdlpx.read() to load MPS files from Python

[ZedongPeng]

Fixes #19

Summary

Adds cupdlpx.read(filename), a gurobipy-style API that loads an MPS file
(plain or .gz) into a Model via the existing C MPS parser:

m = cupdlpx.read("problem.mps")
m.optimize()

OBJSENSE MAXIMIZE in the file sets ModelSense automatically.

Changes

• New read_mps pybind11 binding wrapping read_mps_file(); mps_parser.h gains extern "C" guards.
• mps_parser.c now builds on Windows (strtok_r/strdup MSVC shims), so the CMake exclusion is removed.
• Tests (test/test_read_mps.py) and README docs.
• Unrelated fix: feasibility-polishing summary no longer prints when verbose is off.