phsl / new-api

The previous commit commented out AddOtherRatio("n") in the Ali
adaptor to fix double-counting but this could cause billing evasion
when n is specified via extra["parameters"] instead of request.N.

Root cause: ImagePriceRatio in GetTokenCountMeta() already included
n, AND channel adaptors added OtherRatio("n"), resulting in n²
billing.

Proper fix:
- Remove n from ImagePriceRatio (keep sizeRatio * qualityRatio only)
- In ImageHelper, add default OtherRatio("n") when adaptor hasn't
  set one; set fallback tokens to 1 (base unit)
- Restore Ali adaptor's AddOtherRatio("n") — it uses actual upstream
  parameters/response count, preventing billing evasion