fix(forkchoice): include fresh gossip aggregates in proposals

[zclawz]

Summary

Fixes a live fork-choice/proposal packaging gap exposed by Hive client-interop run 1784788366-5a62c8c486eb2725285e622f60315e02.

The run was already using a devnet5 image containing PR #1055, but these failures are a different class: non-aggregator proposers could receive valid aggregate gossip, keep it in latest_new_aggregated_payloads, and still build blocks from only latest_known_aggregated_payloads before the interval-4 promotion pass moved the payload over.

Changes

• Proposal candidate selection now considers both promoted and freshly validated aggregate payloads.
• Proposal proof packaging greedily selects coverage from both payload pools.
• Proposal coverage attribution includes fresh gossip payloads so logs do not report gossip=none for selected fresh aggregates.
• Added regression coverage for interval-0 selection of fresh gossip payloads and a full getProposalAttestationsPreAggregated path check.

Validation

• /tmp/zig-x86_64-linux-0.16.0/zig fmt --check pkgs/node/src/forkchoice.zig
• git diff --check
• /tmp/zig-x86_64-linux-0.16.0/zig build --fetch --summary none
• /tmp/zig-x86_64-linux-0.16.0/zig build all --fetch --summary none

Attempted full zig build test --summary all with Zig 0.16.0, but this container still cannot run the test target because rustup is missing:

error: failed to spawn and capture stdio from rustup: FileNotFound
failed command: rustup run nightly cargo ... -p zeam-glue ...

Before that external failure, the already-started preset/utils/metrics test groups passed, matching the previous environment limitation.

Hive run investigated: https://hive.leanroadmap.org/suite.html?suiteid=1784788366-5a62c8c486eb2725285e622f60315e02.json&suitename=client-interop&client=zeam_devnet5

[zclawz]

Status: PR opened for the Hive client-interop aggregation/proposal packaging failure.

What changed:

• Proposal selection now includes validated fresh gossip aggregates from latest_new_aggregated_payloads, not only promoted latest_known_aggregated_payloads.
• Proposal proof packaging selects from both pools.
• Coverage logging now attributes selected fresh gossip payloads correctly.
• Added regressions for interval-0 fresh gossip payload selection and the getProposalAttestationsPreAggregated path.

Validation:

• /tmp/zig-x86_64-linux-0.16.0/zig fmt --check pkgs/node/src/forkchoice.zig passed
• git diff --check passed
• /tmp/zig-x86_64-linux-0.16.0/zig build --fetch --summary none passed
• /tmp/zig-x86_64-linux-0.16.0/zig build all --fetch --summary none passed
• zig build test --summary all was attempted with Zig 0.16.0 but this container still stops before the touched test module because rustup is not installed (failed to spawn ... rustup: FileNotFound).

Hive reference: https://hive.leanroadmap.org/suite.html?suiteid=1784788366-5a62c8c486eb2725285e622f60315e02.json&suitename=client-interop&client=zeam_devnet5