Guard deprecated concat copy keyword by pandas version in BatchExample.py

[xyf5432]

Fixes #647

Changes

Guard the deprecated copy keyword of pd.concat by pandas version in
scripts/BatchExample.py, so behaviour is preserved on every supported
version:

• scripts/BatchExample.py: module-level
  PANDAS_VERSION = Version(pd.__version__) (from packaging, already a
  transitive dependency of pandas), and

  if PANDAS_VERSION < Version("3.0"):
      agg = pd.concat([agg, frame], copy=False)
  else:
      agg = pd.concat([agg, frame])

  — the same pattern as Fix pandas 3 string dtype compatibility and CI flakes NVIDIA/cuml#8142.

Verification

The copy keyword never affects the result of concat on any
pandas version, only whether input buffers are copied; the branch keeps
that behaviour exactly as it was on each side of the boundary. Runtime
checks in isolated venvs:

• pandas 2.3.3 takes the copy=False branch: identical results to
  today's code (per-run row accumulation across *_job_* csvs), no
  warning.
• pandas 3.0.5 takes the plain branch: no Pandas4Warning is emitted,
  results identical (the copy keyword is a documented no-op under
  Copy-on-Write).
• Modified file passes python -m py_compile.