fix(examples): standardize explicit resource cleanup

[cpcloud]

Summary

Closes#1676.

• apply deterministic cleanup in cuda_core examples using try/finally so streams, buffers, and graph resources are always released
• extend cuda_bindings/examples/common/common.pyKernelHelper with explicit lifetime management (close, context-manager support) and deterministic NVRTC program teardown
• update bindings examples to explicitly close helper-owned modules and clean up missed resources (including missing stream/event teardown in simpleCudaGraphs_test.py)
• align example behavior with issue Examples: Standardize resource cleanup #1676 guidance to avoid relying on process-exit cleanup

Test plan

• pixi run --manifest-path cuda_core -e cu13 python -m compileall <all touched example/helper files>
• pixi run --manifest-path cuda_core -e cu13 pytest cuda_core/tests/example_tests/test_basic_examples.py -q

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[cpcloud]

/ok to test

[cpcloud]

/ok to test

[cpcloud]

/ok to test

[cpcloud]

/ok to test

[mdboom]

Approved, modulo fixing whatever is causing the tests to fail.

Not something for this PR, because it's clear this PR is trying to only make changes to cuda_bindings/examples. This PR definitely highlights places where cuda.core objects /should/ have context managers, and I will probably create a new issue to identify those and implement them (and then update these examples accordingly at that point).

[cpcloud]

/ok to test

[github-actions]

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