Revise security policy and reporting guidelines

Add Contributor Covenant Code of Conduct

chore: add GitHub issue and PR templates

Merge pull request #20 from fxthiry/release/1.0.0-rc.5

ci: add codecov config with relaxed patch threshold

test: add invalid header name and value validation tests

style: apply rustfmt formatting

chore: bump version to 1.0.0-rc.5 and update changelog

docs(readme): rewrite Why Valerter section for clarity

fix(tracing): use instrument() in all async notifier functions

fix(tracing): use instrument() for async-safe span propagation

fix(logs): promote notification success log to info level

docs(metrics): add valerter_lines_discarded_total metric

Merge branch 'feature/robustness-tcp-keepalive-streambuffer' into release/1.0.0-rc.5

feat(robustness): add TCP keepalive and StreamBuffer size limit