feat: Update Minimum Deployment Targets

[BrandonStalnaker]

Background

• The SDK's minimum deployment targets (iOS 9.0/tvOS 9.0) are significantly outdated. Apple has deprecated many APIs that were required for backward compatibility with these older OS versions, and modern iOS development best practices recommend supporting only actively maintained OS versions.

What Has Changed

• Updated minimum deployment target from iOS 9.0 to iOS 15.6 in the podspec
• Updated minimum deployment target from tvOS 9.0 to tvOS 15.6 in the podspec
• Updated Xcode project build settings to reflect the new deployment targets

Checklist

• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests (existing tests) that prove my fix is effective or that my feature works.
• I have tested this locally.

Additional Notes

• {Any additional information or context relevant to this PR}

Reference Issue (For employees only. Ignore if you are an outside contributor)

• Closes https://rokt.atlassian.net/browse/SDKE-554

The merge-base changed after approval.