* feat(cli): add --v8-flags plumbing to configure V8 at startup (#130)
Obscura had no way to pass flags to V8, so users hitting OOM on pages
larger than ~5MB had no escape hatch. Adds a generic passthrough rather
than a one-off heap knob, so future V8 tuning needs no new code.
- New `obscura_js::set_v8_flags` (Once-guarded, empty-string no-op).
- Global `--v8-flags <FLAGS>` arg with `allow_hyphen_values = true`,
applied once in `main` before any isolate is created.
- Usage: `obscura --v8-flags "--max-old-space-size=4096" fetch <url>`.
Closes#130.
* test(cli): expand --v8-flags coverage with normalize helper
Extract normalize_v8_flags() from main() so the trim/empty-check logic
is unit-testable without needing to invoke V8. Adds parse-coverage tests
for --v8-flags with serve/scrape subcommands and empty-string values,
plus pure-function tests for the normalizer.
