💡 Motivation and Context

This ports the whitespace-trimming fix from posthog-go to posthog-php. It trims surrounding spaces and line breaks from the project API key, personal API key, and host before using them so the SDK does not silently send invalid tokens or build broken endpoints from whitespace-polluted configuration.

💚 How did you test it?

• ./vendor/bin/phpunit --do-not-fail-on-warning --do-not-fail-on-deprecation --do-not-fail-on-phpunit-warning --do-not-fail-on-phpunit-deprecation --filter 'testClientTrimsWhitespaceSensitiveConfig|testClientLogsWhenApiKeyIsEmptyAfterTrimmingWhitespace|testInitDefaultsBlankHostAfterTrimmingWhitespace|testWhitespacePersonalApiKeyFallsBackToFlagsEndpoint'

📝 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

• Added the release label to the PR
• Added exactly one version bump label: bump-patch, bump-minor, or bump-major