0691 — Compaction options are constructed inline

Context

NewCompactionOptions only returned an enabled struct and a nil error. The user requested its removal and inline options at every call site.

Decision

• Supersede the constructor choice in 0612; preserve its message-key placement, explicit Enable flag, rank ordering, and delivery behavior.
• Construct CompactionOptions inline with Enable true and the desired Rank. Omitted Rank is zero. Remove the constructor and its Vulkan alias.
• Keep validation at produce time, including rejection of enabled compaction without a message key and a nonzero rank with Enable false.
• Migrate library callers, examples, benchmarks, and current documentation. Record CompactionOptions as an exception to the constructor convention.

Consequences

Callers no longer handle an error that cannot occur. This is a pre-v1 source API removal; compaction semantics and stored data are unchanged.