Fix attestation inclusion delay calculation

[OkeyAmy]

Closes #14

Summary

• Add attestation inclusion-delay accounting that measures wall-clock slots directly, including skipped slots.
• Add linear inclusion-delay reward calculation with zero reward at delay 32.
• Add consensus branch weighting that consumes wall-clock inclusion-delay rewards.
• Add regression coverage for skipped slots and fork-choice weight invariance across skipped-slot distributions.

Testing

• cargo build --verbose
• cargo test --verbose

[JamesEjembi]

ci failed

[JamesEjembi]

LGTM