fix: add missing bos_token to example templates

[toslunar]

This PR updates chat template examples to align with the latest (>=0.4.3) /v1/chat/completions spec on BOS.

Some chat templates don't contain bos_token, especially when it's written before v0.4.3. According to the excellent investigation #9519, the chat serving does not add BOS again, while awkwardness remains in the offline chat interface (to be fixed).

[github-actions]

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[DarkLight1337]

Thanks for fixing, can you add some unit tests to ensure that the BOS token isn't added twice in this case?

[toslunar]

Added a test.

Is it OK to place it to a new directory (tests/examples_tests) because it seems the first time to test files in examples? I named it examples_tests because it shouldn't be confused with data directories like tests/data and tests/prompts.

[DarkLight1337]

I would just name the directory tests/examples. Can you add the tests to CI by editing this file?

[DarkLight1337]

Let's merge this with the existing Examples Test to avoid starting a new instance just for this.