Add .config/nextest.toml with ci and ci-proptest profiles:
- ci: JUnit output, 60s slow test timeout, retry on flaky tests
- ci-proptest: Higher timeouts, no retries for proptest
Relates to pdftract-5rvp9: Phase 0.3b glibc test leg implementation
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
