feat: add endpoint URL logging for RPC errors

[Copilot]

Problem

When RPC endpoints become unavailable (due to rate limits, connection issues, etc.), the error logs don't explicitly indicate which endpoint is affected. This makes troubleshooting difficult, especially in multi-chain deployments where operators need to quickly identify which specific endpoint is having issues.

Example of the current error log:

Error: HTTP error: 429 Too Many Requests
Location:
    /app/src/chains.rs:435:33

While the chain_id is logged, the actual RPC endpoint URL is missing, requiring operators to cross-reference configuration files to determine which endpoint needs attention.

Solution

This PR adds endpoint URL logging to all RPC error scenarios by:

1. Storing the endpoint URL in the Chain struct - Added an endpoint field and getter method so the URL is accessible throughout the codebase

2. Enhanced transport layer tracing - Modified TraceLayer and TraceTransport to include rpc.endpoint in OpenTelemetry span attributes, ensuring all RPC calls now include endpoint information in their traces

3. Explicit health check logging - Updated the health check error logging to include the endpoint URL alongside chain_id

Impact

After these changes, when an RPC endpoint becomes unavailable, logs will clearly show:

Failed to obtain block number for health check
  err: HTTP error: 429 Too Many Requests
  chain_id: 8453
  endpoint: https://mainnet-preconf.base.org/

This enables operators to:

• Immediately identify which specific endpoint is having issues
• Quickly correlate errors with rate limits, regional outages, or provider-specific problems
• Respond faster to infrastructure issues without manually checking configurations

Testing

• ✅ Code compiles and passes clippy linting
• ✅ All existing tests continue to pass
• ✅ No breaking changes to existing functionality

Fixes #issue_number

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• arb1.arbitrum.io
  • Triggering command: /home/REDACTED/work/relay/relay/target/debug/deps/relay-0116f8e29f20dbc0 (dns block)
• eu-central-mainnet.rpc.ithaca.xyz
  • Triggering command: /home/REDACTED/work/relay/relay/target/debug/deps/relay-0116f8e29f20dbc0 (dns block)
• mainnet.optimism.io

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Additional logging in cases one or multiple rpc endpoints become unavailable</issue_title>
<issue_description>## Description

Additional logging in cases one or multiple rpc endpoints become unavailable.

Problem Statement

At the moment relay does not explicitly log which chain/rpc endpoint is affected. Example error log due to rate limits being hit:

2025-10-01 14:29:54.865	
    /app/src/chains.rs:435:33
2025-10-01 14:29:54.865	
Location:
2025-10-01 14:29:54.865	

2025-10-01 14:29:54.865	
    HTTP error: 429 Too Many Requests
2025-10-01 14:29:54.865	
Caused by:
2025-10-01 14:29:54.865	

2025-10-01 14:29:54.865	
Error: HTTP error: 429 Too Many Requests
2025-10-01 14:29:54.857	
2025-10-01T06:29:54.857867Z  INFO alloy_pubsub::service: Pubsub service request channel closed. Shutting down.
2025-10-01 14:29:54.853	
2025-10-01T06:29:54.853721Z DEBUG alloy_rpc_client::call: sending request method=eth_getBlockByNumber id=5
2025-10-01 14:29:54.850	
2025-10-01T06:29:54.850349Z DEBUG poller{method=eth_getBlockByNumber}:ReqwestTransport{url=https://mainnet-preconf.base.org/}: hyper_util::client::legacy::connect::http: connected to 104.18.40.153:443
2025-10-01 14:29:54.849	
2025-10-01T06:29:54.849754Z DEBUG poller{method=eth_getBlockByNumber}:ReqwestTransport{url=https://mainnet-preconf.base.org/}: hyper_util::client::legacy::connect::http: connecting to 104.18.40.153:443
2025-10-01 14:29:54.844	
2025-10-01T06:29:54.844756Z DEBUG poller{method=eth_getBlockByNumber}:ReqwestTransport{url=https://mainnet-preconf.base.org/}: reqwest::connect: starting new connection: https://mainnet-preconf.base.org/
2025-10-01 14:29:54.844	
2025-10-01T06:29:54.844695Z DEBUG alloy_rpc_client::call: sending request method=eth_getBlockByNumber id=4
2025-10-01 14:29:54.844	
2025-10-01T06:29:54.844683Z DEBUG alloy_rpc_client::call: sending request method=eth_chainId id=3
2025-10-01 14:29:54.844	

Implementation Hints

User story

• Easier troubleshooting
  </issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #1448

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