Update all integration tests to use run/Runner terminology
Mechanical rename across 106 .txtar test files plus supporting Go files:
- cog predict → cog run (prediction commands)
- cog run → cog exec (arbitrary command execution in 6 files)
- predict: 'predict.py:Predictor' → run: 'run.py:Runner' (cog.yaml)
- -- predict.py -- → -- run.py -- (txtar file sections)
- from cog import BasePredictor → from cog import BaseRunner
- class Predictor(BasePredictor) → class Runner(BaseRunner)
- def predict(self → def run(self
- Updated comments and docstrings to use runner terminology
- integration-tests/README.md: updated examples and descriptions
- integration-tests/concurrent/concurrent_test.go: updated config and code
