feat(schema): add VAST 4.4 to the VAST version enum

[aleksUIX]

Summary

• enums/vast-version.json now includes 4.4. IAB already hosts vast_4.4.xsd and CTV tags already declare version="4.4", so a truthful manifest currently fails validation.
• Tracker version gates that already include 4.3 also accept 4.4. fullscreen / exitFullscreen stay 2.x/3.x-only.
• The 4.4 XSD is still annotated DRAFT for working group discussion. This change accepts the version attribute; it does not claim IAB has published a final specification.

pre-change  (2.0-4.3): vast_version "4.4" -> REJECTED
post-change (2.0-4.4): vast_version "4.4" -> ACCEPTED

Test plan

• tests/creative-delivery-contracts.test.cjs
• tests/tracker-execution-contracts.test.cjs
• precommit unit + server unit + typecheck

I have read the IPR Policy.

[bokelley]

Thanks for the thorough implementation and for surfacing the real data-integrity question. We are keeping the 3.2 enum to published VAST versions and deferring 4.4 to #7247. We will revisit for AdCP 3.3 when IAB publishes the final specification/schema or an independent adopter brings a concrete interoperability test that needs a truthful version="4.4" declaration.