Some bugfixes for SolverHighs

[rschwarz]

• handle error case for var_by_name (did not check status)
• properly reset objective before setting new coefficients (before just updated new coefficients, keeping old)
• add some comments as a reminder that HiGHS doesn't recognize BINARY variables as separate from INTEGER
• fix ctypes and type annotations for boolean option getter and setter

[rschwarz]

Tests are failing because of the GRBloadenv bug described in #398.

Even without Gurobi, some HiGHS tests are falling (in test/mip_files_test.py) because:

Running HiGHS 1.9.0 (git hash: fa40bdf): Copyright (c) 2024 HiGHS under MIT licence terms
ERROR:   HiGHS build without zlib support. Cannot read .gz file.
ERROR:   Model file /home/robert/src/python-mip/test/data/p0282.mps.gz not supported

This is with highspy from PyPI.