fix(linux): make CDP framing linear

[yashranaway]

Closes #19

Summary

• frame NUL-terminated DevTools messages with a persistent scan cursor
• amortize consumed-prefix compaction instead of shifting the buffer on every read
• cover the production 8 KiB chunk pattern with a 30 MiB regression payload
• mark roadmap backlog item A8 complete

Validation

• npx --yes pnpm@9.15.0 test:runtime
• Swift 6.1 protocol suite in Docker (41/41)
• npx --yes pnpm@9.15.0 test:e2e:linux
• git diff --check