Update price to get price from pyth api

[bbalser]

Summary

Switch the price service from reading HNT prices on-chain (via Solana RPC + helium-lib Pyth account
reads) to pulling them directly from the Pyth Hermes HTTP API. The Hermes URL (including the HNT feed id) is
configurable via the existing source setting.

Multi-token support is dropped — the service now emits HNT prices only. The solana path dependency is
removed from the price crate entirely, and unused workspace deps are trimmed.

Changes

• HTTP fetcher: PriceGenerator now holds a reqwest::Client and fetches
  /v2/updates/price/latest?ids[]=<hnt_feed_id>. The parsed response is scaled by 10^(HNT_DECIMALS + expo)
  to preserve the same u64 integer semantics (price × 10^8) that downstream consumers expect. Stale-price
  fallback, file caching, metrics, and the 60s poll cadence are unchanged.
• Settings (price/src/settings.rs):
  • Dropped TokenSetting / tokens Vec and the JSON-or-struct deserializer helper.
  • Promoted default_price to a top-level optional field (for testing).
  • source now defaults to the Hermes HNT endpoint.
• price check CLI (price/src/cli/check.rs): rewrote to fetch Hermes once and print the feed id, raw
  price, confidence, exponent, publish time, and the scaled integer the daemon would emit. Takes an optional
  --url override; otherwise uses the source setting.
• main.rs: removed the per-token spawn loop; one PriceGenerator is started. Check args reduced to
  --url.
• metrics.rs: hardcoded token_type = "hnt"; dropped solana::Token.
• Cargo.toml:
  • Added reqwest = { version = "0.12", features = ["json"] } (pinned locally, mirroring helium_iceberg).
  • Removed solana = { path = "../solana" }.
  • Removed unused deps: thiserror, futures-util, prost, tracing-subscriber, tokio-util,
    metrics-exporter-prometheus, rust_decimal_macros.
• pkg/settings-template.toml: replaced Solana RPC URL with the Hermes URL; removed [cluster] section
  and legacy per-token commented fields.
• README.md: updated to describe the Hermes HTTP flow.