[codex] draft svg buffer parser refactor

[lovasoa]

Summary

Draft snapshot of the SVG persistence parser refactor. This moves stored SVG scanning toward buffer-backed elements, lazy attribute/text/path reads, and writer-owned stored attribute order.

This is intentionally marked draft because the current shape is not merge-ready and still needs simplification/review before landing.

Notes

• Streaming parser now yields buffer-backed element/suffix objects.
• Stored element IDs are read eagerly; other data stays lazy.
• Persistence rewrite can preserve raw source buffers for clean items.
• Tool contracts now expose stored attribute order for parser reuse.

Validation

• npm test
• npm run bench