michie (pronounced /'mikɪ/) — an attribute macro that adds memoization to a function

For the past few months I have been participating in Mobus Operandi, a small community for regular study of Rust in remote mob programming format.
We have recently published michie, the first product of the work done in this community.

Even though it makes use of static mut and type casting and involves hygiene and type inference workarounds, this is the first rust crate for most of the co-authors.
We have the intention and hope that michie will be helpful and widely used.
Therefore we would appreciate any and all feedback from the Rust community.

Some areas where we feel that despite our best efforts, something might have slipped past us are:

• use of static mut
• API design
• the trait object and downcasting
• if any of the documentation is unclear to you