Adds Counter class to counter.py

[opencode-agent]

I've added the new file counter.py at the repo root with a Counter class that includes:

• increment(amount=1)
• decrement(amount=1)
• get_value()

Usage example:

• c = Counter()
• c.increment()
• c.increment(5)
• c.decrement(2)
• value = c.get_value() # 4 in this example

If you want a different interface (e.g., read-only value attribute, or initialization from an external config), I can adjust quickly.

Closes #697

opencode session  |  github run