🎯 Problem to be solved

The infosync proposal topic negotiates the cluster-wide supported block proposal types (builder/synthetic/full) every epoch, but its result is dead code. infosync.Proposals() has had no callers since #1762 (Feb 2023), which disabled the dynamic cluster-wide builder-API toggle because VCs cannot be reconfigured at runtime. The builder-vs-full decision is now driven entirely by static config (--builder-api → builder_boost_factor pre-gloas, charon's BuilderConfig from the gloas fork). The topic therefore costs a priority exchange each epoch for a value nobody reads.

🛠️ Proposed solution

Remove the dead proposal topic and its supporting code: topicProposal, Component.Proposals, the proposals field and proposalsToStrings in core/infosync, app.ProposalTypes, and the now-unused core.ProposalType constants. Dropping the topic is backward compatible: the priority protocol treats topics as arbitrary and scores each independently, so a topic sent by fewer than quorum peers simply drops out of the result during a mixed-version rollout, with no effect on the version and protocol topics.