[reffers] Data races in reffers

An issue was discovered in the reffers crate through 2020-12-01 for Rust. ARefss can contain a !Send,!Sync object, leading to a data race and memory corruption.

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-36203
• https://github.com/diwic/reffers-rs/issues/7
• https://rustsec.org/advisories/RUSTSEC-2020-0094.html
• https://github.com/advisories/GHSA-39xg-8p43-h76x