Add Requesty to APIProvider

[Thibaultjaigu]

Summary

Adds a .requesty case to APIProvider (raw value "requesty", display name "Requesty") and lists it in selectableProviders right after .openRouter.

Context

This is the enum half of re-adding Requesty to Agent! properly, following the removal in AgentiLoop/Agent#25 (the earlier attempt only touched the app and was never wired end to end). The app side is in AgentiLoop/Agent#49 and needs this case to compile, so a tag on this package after merge would let the app PR build against it.

Requesty is an OpenAI-compatible router at https://router.requesty.ai/v1 (models list at /v1/models, provider/model ids such as openai/gpt-4o-mini), so the app wires it through the same OpenAI-compatible path as OpenRouter and MiniMax.

Verified with swiftc -typecheck on the package sources.

Disclosure: I work at Requesty. Happy to adjust anything to match project conventions.

[AgentiLoop]

Updated AgentTools and Agent repos. We will probably move APIProvider.swift to the main app in a future update and try to consolidate some of these entries, but not today. There is some risk involved.