[Bug] blockHashFromNumber returns null with no log when the node doesn't have the network (e.g. query nodes)

Bug report

IndexNodeResolver::block_ptr_for_number returns Ok(None) without logging when the network isn't in the node's BlockchainMap. blockHashFromNumber on a node without that network is therefore an instant null, and from outside that looks the same as "block not found".

The common case is a query node. A node whose id matches [general] query gets Networks::noop() in from_config_inner, so it has no chains at all. It still serves the index-node API on 8030 and answers version, and nothing at startup says it came up query-only.

indexer-agent pointed at that node reports IE070 no data returned, and people go chasing the RPC and the EBO subgraph. It's the same unanswered question as #4880.

resolve_cached_ethereum_calls already logs Failed to fetch cached Ethereum calls; nonexistent network for the same situation, so blockHashFromNumber is the odd one out.

Repro on v0.45.0:

• [general] query = "index_node_0" with --node-id index_node_0, then { blockHashFromNumber(network: "mainnet", blockNumber: 25961537) } returns null with query_time_ms: 0 and no WARN
• same result on a normal index node with network: "nosuchchain"

Suggestion: a WARN (or a GraphQL error) naming the network and this node's id when the network isn't configured here, and an INFO at startup when a node comes up query-only. Same idea as #6718 for the ingestor.

Relevant log output

INFO Query timing (GraphQL), block: 0, query_time_ms: 0, variables: null, query: { version { version } blockHashFromNumber(network: "mainnet", blockNumber: 25961537) } , subgraph_id: indexnode, component: IndexNodeServer

IPFS hash

No response

Subgraph name or link to explorer

No response

Some information to help us out

• Tick this box if this bug is caused by a regression found in the latest release.
• Tick this box if this bug is specific to the hosted service.
• I have searched the issue tracker to make sure this issue is not a duplicate.

OS information

macOS

Start at IndexNodeResolver::block_ptr_for_number and trace the no-network path through Networks::noop() and from_config_inner. Compare its behavior with resolve_cached_ethereum_calls, then reproduce the blockHashFromNumber query on a query-only or unknown-network node. Done means the missing network is clearly reported with the network and node id, and query-only startup is identified in logs.