feat: advertise configured account heads during discovery

[Cryptoloveer]

Problem

Last-transaction discovery advertises only a random sample of account heads. Operators cannot ensure that locally important accounts are included in each discovery broadcast, so those accounts may take longer to be discovered by peers.

Fix

• Add atto.bootstrap.discovery.hinted-addresses as a local configuration property.
• Resolve configured addresses to their current account heads during each historical-node broadcast.
• Include those heads alongside the existing random sample without changing the wire protocol.
• Skip configured addresses that are not present locally or whose stored algorithm does not match.
• Deduplicate hinted heads that are already present in the random sample.

Validation

• Added a focused test covering a configured head alongside the random sample.
• The test verifies that a hinted head already in the random sample is emitted only once.
• Updated the existing unit-test fixture for the new configuration dependency.
• Awaiting upstream CI before marking the draft ready for review.

Closes #213.

[Cryptoloveer]

The focused implementation and duplicate-head test are now in place, and the branch is synchronized with current main. Could a maintainer approve the fork workflow run so I can confirm the full test suite before marking this ready?