Add pricing for GPT 5.4

[saphitv]

Add pricing data and model for GPT 5.4.

Tiered pricing: $2.50/$15.00 per 1M tokens (≤272k), $5.00/$22.50 (>272k)
caching tiers: $0.25 (≤272k), $0.50 (>272k)
Aliases: gpt-5.4 (not sure if there are others)

[mike1858]

@saphitv I already did this but I didn't make a PR for it. I'll release this when we get your cloud improvements in.