Add H2 connection pool with per-authority multiplexing

## Summary
- Add AuthorityPool<C> that manages multiple H2 connections to a single authority (scheme+host+port), creating connections on demand when streams are exhausted and evicting failed ones
- Add Pool<C> that routes requests to the correct AuthorityPool via a DashMap<ConnectionInfo, AuthorityPool<C>>
- Add PoolBuilder with configurable max_connections and init_max_streams per authority

Author: muhamadazmy

Cargo.lock

@@ -25,6 +25,8 @@ base64 = { workspace = true }
 bs58 = { workspace = true }
 bytes = { workspace = true }
 bytestring = { workspace = true }
+dashmap = { workspace = true }
+derive_builder = { workspace = true }
 futures = { workspace = true }
 h2 = "0.4.12"
 http = { workspace = true }