Allow --bootnodes to read enode URLs from file or remote URL

[gap-editor]

PR description

This change enhances the --bootnodes option so it can read enode URLs from a file or remote source, in addition to the existing comma-separated CLI argument. Specifically:

• Introduce a new helper method resolveBootnodeStrings to handle:
  • HTTP(S) URLs (fetch and parse each line)
  • file:// URIs
  • Local file paths
  • Fallback to raw enode strings when no file or URL is detected
• Update the bootnodes parsing logic to first resolve all inputs via the helper, then pass the flattened list into buildEnodes.
• Provide clear error messages if fetching or reading any of the sources fails.

This enables workflows like Ephemery’s dynamic download of latest enodes at runtime:

--bootnodes=https://ephemery.dev/latest/metadata/enodes.txt

Fixed Issue(s)

fixes #8538

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• Checked out our contribution guidelines?
• Considered documentation and added the doc-change-required label to this PR if updates are required (docs).
• Considered the changelog and included an update if required (changelog).
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• spotless: ./gradlew spotlessApply
• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests

[github-actions]

This pr is stale because it has been open for 30 days with no activity.

[github-actions]

This pr was closed because it has been inactive for 14 days since being marked as stale.

[macfarla]

@gap-editor apologies for the delay in reviewing your PR. Are you still interested in getting this over the line? If so -

• would be nice to see unit tests added
• also consider some logging at least at DEBUG level, to make it obvious what's happening

if you've moved on, we can prob get someone from the team to pick this up.

I tested that it works with

besu --network=ephemery --bootnodes=https://ephemery.dev/latest/metadata/enodes.txt
...
2025-07-24 15:05:28.424+10:00 | main | INFO  | RunnerBuilder | Resolved 2 bootnodes.

besu --network=ephemery --bootnodes=https://ephemery.dev/latest/metadata/enodes.txt,enode://50a54ecbd2175497640bcf46a25bbe9bb4fae51d7cc2a29ef4947a7ee17496cf39a699b7fe6b703ed0feb9dbaae7e44fc3827fcb7435ca9ac6de4daa4d983b3d@137.74.203.240:30303
...
2025-07-24 15:05:28.424+10:00 | main | INFO  | RunnerBuilder | Resolved 3 bootnodes.

[macfarla]

Other suggestions for the benefit of anyone picking this up

• refactor to make it a separate class rather than adding methods to BesuCommand directly
• add some unit tests

[github-actions]

This pr is stale because it has been open for 30 days with no activity.

[macfarla]

closing as this is superseded by #9097