types/block.zig: evaluate or remove finishSingleRawAggregatePrep degenerate fast-path

[zclawz]

Context

Raised by @ch4r10t33r in PR #925 review.

finishSingleRawAggregatePrep in pkgs/types/src/block.zig is a degenerate-shape fast-path for 1 gossip sig + 0 children that still invokes leanMultisig once but skips child-selection loops entirely.

Action Required

• Measure whether this path provides a meaningful performance improvement compared to the general path
• If the improvement is negligible or unmeasurable under realistic conditions: remove the code and use the general path only (simpler, less surface area)
• If there is a clear improvement: document it with a benchmark and keep it

Related

• PR node, types, xmss: keep aggregate worker under 4s slot budget (#907) #925: node, types, xmss: keep aggregate worker under 4s slot budget
• /cc @ch4r10t33r @g11tech