Filtered highlights from issue 668:

• tokio-rcu is the featured crate: a user-space RCU implementation designed around async Rust and Tokio.
• The compiler work includes denser Polonius state and normalization improvements; library work adds custom-allocator support to UniqueArc/UniqueRc and stabilizes smart-pointer mapping.
• Cargo has a new checksum-freshness tracking issue, more lint documentation, better Git retry behavior, and a theoretical use-after-free fix in the parser.

I skipped the routine PR list and contributor tasks.