Small serverless model rate-limit ceilings doubled, to 216M total prompt TPM

We doubled the adaptive rate-limit ceilings for Small serverless models.

The Small tier now has these ceilings:

• Total Prompt TPM: 216M
• Uncached Prompt TPM: 54M
• Generated TPM: 2.16M

Medium and Large model ceilings are unchanged. Serverless rate limits now also lists which tier each Serverless model falls in.