fix: validate top-level event uuids

[marandaneto]

💡 Motivation and Context

Top-level event uuid values can be passed through capture/raw payloads, but invalid values were sent unchanged. This validates supplied UUIDs and replaces invalid values with a generated UUID v4 so queued events keep a valid event identifier.

💚 How did you test it?

• ./vendor/bin/phpunit --no-coverage test/PostHogTest.php --filter 'Uuid|TopLevelUuid'
• ./vendor/bin/phpunit --no-coverage
• composer api:check
• php -l lib/Client.php && php -l lib/PostHog.php && php -l test/PostHogTest.php

📝 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

• Generated a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Pi coding agent implemented the requested UUID validation in a dedicated worktree. The change keeps valid supplied UUIDs, replaces invalid top-level uuid values for capture() and raw() payloads with generated UUID v4 values, documents the behavior in the PHPDoc, and adds parameterized coverage for valid UUID versions v1-v8 plus invalid fallback cases.

[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
test/PostHogTest.php:730-758
**Prefer parameterised tests for invalid-UUID coverage**

The team rule is to always prefer parameterised tests. `testCaptureReplacesInvalidTopLevelUuid` only exercises one invalid value (`"not-a-uuid"`), and `testRawReplacesInvalidTopLevelUuid` only tests `false`. A PHPUnit `@dataProvider` over `capture()` and `raw()` separately would let you cover `null`, `""`, `0`, `false`, `"not-a-uuid"`, and nil UUIDs without repeating the assertion boilerplate, and it makes the intent of each case explicit at a glance. Similarly, `testCaptureKeepsValidTopLevelUuid` only checks one valid value; a data provider covering v1, v4, v7, etc. would confirm the regex boundary correctly.

_{Reviews (1): Last reviewed commit: "fix: validate top-level event uuids" | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "test: parameterize uuid validation cover..." | Re-trigger Greptile}