feat(synthetic): add pricing

[Amolith]

• Synthetic's API doesn't include pricing (yet), so this adds manual overrides from their pricing page
  • Cached rates are set equal to the regular rates because they don't have separate cached rates afaict
• Generates synthetic-promax.json for Synthetic Pro or Synthetic Max subscribers based on the provider we're already generating, just with prices set to 0
• Adds metadata override for DeepSeek V3.2 to indicate it supports reasoning

Assisted-by: Claude Opus 4.5 via Crush

• I have read CONTRIBUTING.md.
• [~] Kujtim and I discussed the pricing override, but not the metadata override for DS V3.2 or the new provider covering the Synthetic subscription

[Amolith]

These changes are now based on #138

[Amolith]

Rebased on main, also changed the default large model to GLM 4.7

[meowgorithm]

Awesome. @Amolith and @kujtimiihoxha: are we good to merge this one?

[Amolith]

@meowgorithm actually, not quite yet. I was digging into Synthetic's API some more for a different thing and noticed that they do provide pricing, so the overrides aren't needed. Working on a refactor

[Amolith]

Hardcoded prices removed, ready for review.

@kujtimiihoxha and I were talking separately about in-Crush ways of handling the pro/max subcription bits thinking it was predicated on API changes. However, their /quotas endpoint is actually sufficient for differentiating between a key billed at subscription vs API rates. Should we remove the subscription provider generation from this PR and just do the enhancement in Crush, or merge this one then delete (or something else) the provider once Crush has specific Synthetic subscription handling? I think I'm inclined towards removing subscription generation from this and just handling it in Crush; introducing a provider to Catwalk with near-term plans to remove it seems odd and might require some form of backwards compatibility work.

[kujtimiihoxha]

@Amolith I think we can remove the subscription based provider and just handle detecting if its a subscription user in crush.

We need to do similar things for z.ai and other subscription users and long term probably even show usage limits for these if the provider shows them.

[Amolith]

@kujtimiihoxha yep, that makes sense. I removed subscription generation 👍