Keep mVMC NSROptItrSmp default positive

[tmisawa]

Summary

• Clamp the mVMC standard-mode default NSROptItrSmp to at least 1
  in the C StdFace implementation.
• Apply the same default handling to the Python writer on develop.
• Add regression coverage for NSROptItrStep = 2, where integer division
  previously produced NSROptItrSmp = 0.

Motivation

The mVMC standard-mode default for NSROptItrSmp is derived from
NSROptItrStep / 10. For short optimization runs such as
NSROptItrStep = 2, integer division made the generated modpara.def
contain:

NSROptItrSmp   0

NSROptItrSmp is documented as a positive integer, and a zero averaging
window can lead to invalid optimized-parameter output. This PR keeps the
default positive while preserving the existing default for normal runs
where NSROptItrStep >= 10.

Tests

cmake -S . -B <build-dir> -DMVMC=ON -DTestStdFace=ON -DCMAKE_POLICY_VERSION_MINIMUM=3.5
cmake --build <build-dir> -j2
ctest --test-dir <build-dir> -R HubbardChainShortSROpt --output-on-failure
ctest --test-dir <build-dir> --output-on-failure
PYTHONPATH=python pytest test/unit/test_common_writer.py -q
PYTHONPATH=python pytest test/unit -q