feat: add Curve LP virtual-price fallback to price warmup

[matheus1lva]

Summary

Curve LP tokens that DefiLlama can't price leave a gap in the underlying price
table, and that gap cascades into every derived vault price built on top of
them. This adds an on-chain fallback: when DefiLlama has no price for an
underlying, the warmup prices the Curve LP from its pool's get_virtual_price
scaled by coin0's USD price, filling the gap before derived prices compute.

Changes

• src/curve.ts (new): priceCurveLpUsd resolves a token's Curve pool via
  the AddressProvider registry and prices it as get_virtual_price() / 1e18 * price(coin0). Registry and pool lookups are memoized. Returns null for
  non-registered LPs or when coin0 has no price, so callers treat it as a clean
  miss.
• scripts/warmup-prices.ts: new warmCurveFallbackPrices phase runs
  between the direct and derived phases. It only attempts timestamps that
  neither defillama nor a prior curve run already filled (today always
  refreshes), so repeat runs skip work already on disk.
• src/rpc.ts: add memoized getChainClient(chainId) that reads
  RPC_URL_<chainId>. Both warmup phases drop their per-function client and
  block-number maps in favor of it and the existing cache inside
  estimateBlockByTimestamp, removing two redundant cache layers.
• src/types.ts: register curve in SOURCE_PRIORITY, ranked below market
  sources and above derived, so derived vault pricing consumes a curve
  underlying when no better source exists.

Testing

• bun run typecheck passes.
• No test suite in repo. A reviewer should confirm a known DefiLlama-unpriceable
  Curve LP gets a row with source=curve, and that the derived phase picks up
  that underlying when building the vault price.