Add optional name argument to hello.py greeting script

[Copilot]

hello.py printed a static Hello World with no argument support. This updates it to accept an optional name and use proper greeting formatting.

Changes

• hello.py: Adds greet(name) function returning Hello, {name}!; reads sys.argv[1] as optional name with whitespace-stripped fallback to "World"

python3 hello.py          # Hello, World!
python3 hello.py Alice    # Hello, Alice!
python3 hello.py "   "    # Hello, World!

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