Replace treasury data fetch with subgraph query

[rickstaa]

Is your feature request related to a problem?

Right now we use RPC calls to get information about treasury proposal (see

explorer/pages/api/treasury/proposal/[proposalId]/state.tsx

Line 71 in 5e54fca

const votes = await l2PublicClient

). This makes the endpoint sensitive to RPC outages, rate limits, and node lag.

Describe the solution you'd like

Since treasury proposal + voting information does not need to be strictly real-time on a per-block basis, it’s a good candidate to move over to the Livepeer Subgraph when this upstream pull request has been merged.

Describe alternatives you've considered

No response

Additional context

No response