[FSSDK-12610] chore: Prepare release 4.0.3

[Tamara-Barum]

Summary

• Bumps SDK version from 4.0.2 to 4.0.3
• Updates CHANGELOG.md with changes since 4.0.2
• Updates SDK_VERSION constant and corresponding test

Changes since 4.0.2

• Fix: PHP 8.4 implicit nullable parameter deprecation warnings [FSSDK-12610] Fix: PHP 8.4 implicit nullable parameter deprecation warnings #296
• Security: Fix curl|bash vulnerability in SourceClear scan [FSSDK-12316] [Security] Fix curl|bash vulnerability in SourceClear scan #294

Jira

FSSDK-12610

Files changed

File	Change
src/Optimizely/Event/Builder/EventBuilder.php	SDK_VERSION → '4.0.3'
tests/EventTests/EventBuilderTest.php	client_version → '4.0.3'
CHANGELOG.md	Added 4.0.3 section

Post-merge steps

• Create git tag 4.0.3 on master after merge
• Verify Packagist picks up the new version
• Optionally create a GitHub Release from the tag

🤖 Generated with Claude Code

[coveralls]

coverage: 97.336%. remained the same — tbarum/FSSDK-12610-prepare-release-4.0.3 into master

[Mat001]

Release version correctly updated, Changelog has correct release dat of teh day of the release, changelog descriptive and clear, PR links added.