feat: add reth-based ERC-8004 indexer

[bussyjd]

Summary

• add a standalone Reth-based ERC-8004 indexer package with an embedded ExEx, SQLite/WAL storage, and a thin 8004scan-shaped HTTP API
• update the autoresearch coordinator to prefer an internal indexer via OBOL_INDEXER_API_URL and fall back to SCAN_API_URL when the local service is unavailable or unhealthy
• wire custom Reth image and embedded indexer settings into the Ethereum network template, with install-time validation for the Reth-only path

Scope note

• this PR does not add a self-hosted Base or Base Sepolia node template; Base remains facilitator/payment-only in the current rollout, and discovery can continue to use 8004scan unless an internal indexer is explicitly deployed

Testing

• cargo test --manifest-path /Users/bussyjd/Development/Obol_Workbench/obol-stack/.codex/worktrees/reth-indexer/reth-erc8004-indexer/Cargo.toml
• python3 -m unittest tests.test_autoresearch_coordinator tests.test_autoresearch_persona_flows
• go test ./internal/network

[OisinKyne]

Needs to be a reth archive node beneath erpc too. Haven't a strong decision on the rest of the indexing code. (e.g. if its an exex it probably can't talk through erpc. Is that worht it versus something like ponder instead