Examples: Standardize resource cleanup

[rparolin]

Parent issue: #1673

Goal

Decide on and apply a consistent resource cleanup policy across all examples.

Current state

• Most examples do NOT close streams or buffers explicitly.
• Only saxpy.py and memory_ops.py demonstrate explicit close() calls.
• strided_memory_view_gpu.py uses a finally block for cleanup, others don't.
• No examples use context managers for resource management.

Decisions needed

1. Should examples demonstrate explicit close() calls as best practice?
2. Should examples use context managers (if the API supports them)?
3. Should examples use try/finally blocks for cleanup?
4. Is it acceptable for simple examples to rely on process exit for cleanup?

Files affected

All 25 example files listed in #1673.

[mdboom]

Should examples use context managers (if the API supports them)?

100%. This is the Python best practice.

Is it acceptable for simple examples to rely on process exit for cleanup?

I would say no, not for technical reasons, but because examples tend to be copied-and-pasted into larger things where it would matter.