Add post-processing tool: clean and plot CSV data

hioki-clean clean <file> - removes error rows and settle artifacts
after auto-range transitions. hioki-clean plot <file> - visualizes
CSV data with grouped subplots (voltage, current, power, efficiency).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -10,5 +10,13 @@ dependencies = [
     "pyvisa-py>=0.8.1",
 ]
 
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["hioki3193"]
+
 [project.scripts]
 hioki = "hioki3193.cli:main"
+hioki-clean = "hioki3193.postprocess:main"