0.20 -> 0.21

Summary:
1. Update Cargo.toml to 0.21.0 `rerun_c = { version = "0.21.0", artifact = "staticlib" }`
2. `fbcode/common/rust/tools/reindeer/vendor`
3. Update fixups for arrow and pool-promise
3.a. Ran `fbcode/common/rust/tools/reindeer/buckify`
3. `buck2 build fbsource//third-party/rust:rerun_c`
4. `buck2 run fbcode//scripts/shaynefletcher/project/rerun:rerun_test`

Reviewed By: capickett, jeongseok-meta

Differential Revision: D67542150

fbshipit-source-id: 50a429ae0aa47ba3aa8caf0fc0161dc922f151e4