Codec roadmap: performance gates + CI coverage

[bbopen]

Goal

Add performance gates and CI coverage for new codec paths, per docs/codec-roadmap.md.

Scope

• Define performance budgets for encode/decode paths.
• Add CI coverage for codec suites.
• Add size limit tests and regression coverage for payload scaling (artifact/chunked transport) once implemented.

Acceptance criteria

• Performance budgets are documented and enforced in CI.
• New codecs have dedicated CI coverage.
• Regression tests cover size limits and failure modes.

References

• docs/codec-roadmap.md

[bbopen]

Roadmap updated in docs/codec-roadmap.md. Perf/CI work should cover size-limit tests and the future payload scaling path (artifact/chunked transport) in addition to existing codec suites.