fix: Generate UUID v7 identifiers

[marandaneto]

💡 Motivation and Context

SDK-generated identifiers should use UUID v7 so event UUIDs, personless fallback distinct_ids, and AI telemetry trace/span IDs are time-sortable and consistent with other PostHog SDKs.

💚 How did you test it?

• uv run --extra test pytest posthog/test/test_uuid_utils.py posthog/test/test_client.py::TestClient::test_basic_capture posthog/test/test_client.py::TestClient::test_capture_without_distinct_id_generates_uuid_v7_personless_distinct_id posthog/test/ai/test_uuid_generation.py
• uv run --extra test python -m compileall -q posthog/client.py posthog/_uuid.py posthog/ai
• uvx ruff check posthog/_uuid.py posthog/client.py posthog/ai/openai/openai.py posthog/ai/openai/openai_async.py posthog/ai/anthropic/anthropic.py posthog/ai/anthropic/anthropic_async.py posthog/ai/gemini/gemini.py posthog/ai/gemini/gemini_async.py posthog/ai/claude_agent_sdk/client.py posthog/ai/claude_agent_sdk/processor.py posthog/ai/utils.py posthog/test/test_client.py posthog/test/test_uuid_utils.py posthog/test/ai/test_uuid_generation.py
• uvx ruff format --check posthog/_uuid.py posthog/client.py posthog/ai/openai/openai.py posthog/ai/openai/openai_async.py posthog/ai/anthropic/anthropic.py posthog/ai/anthropic/anthropic_async.py posthog/ai/gemini/gemini.py posthog/ai/gemini/gemini_async.py posthog/ai/claude_agent_sdk/client.py posthog/ai/claude_agent_sdk/processor.py posthog/ai/utils.py posthog/test/test_client.py posthog/test/test_uuid_utils.py posthog/test/ai/test_uuid_generation.py
• uv run --extra dev python .github/scripts/check_public_api.py

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

An implementation agent updated Python SDK-generated UUID fallbacks to use a private UUID v7 helper. The helper uses Python 3.14+ uuid.uuid7() when available and otherwise falls back to a local RFC 9562-compatible implementation for supported older Python versions.

A changeset file was added manually because this is a patch-level SDK behavior fix.

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 1
posthog/test/test_uuid_utils.py:6-12
**Fallback path not explicitly tested**

`test_uuid7_generates_version_7_uuid_string` exercises whichever branch the current Python runtime enters — on 3.14+ only the stdlib path runs; the hand-rolled RFC 9562 implementation is exercised only on older Pythons. A bug in the fallback (e.g. wrong bit-shift for `rand_a`) would pass in CI if tests are run under Python 3.14+. The project also prefers parameterised tests; adding a fixture that patches `uuid.uuid7` away would ensure both paths are always validated, regardless of the runtime used in CI.

_{Reviews (1): Last reviewed commit: "fix: generate UUID v7 identifiers" | Re-trigger Greptile}