[Task] document callback_unwrap

[dj8yfo]

Background

Callback_unwrap can link to [PromiseOrValue] abstraction https://github.com/near/near-sdk-rs/blob/master/examples/cross-contract-calls/high-level/src/lib.rs#L26

User Story

Should have an anchor under #[near] macro doc with description of how it works and a few examples, and with links within repo, how it's used.

   near-sdk-rs
   ├──examples
   │  ├──cross-contract-calls
   │  │  └──high-level
   │  │     └──src
   │  │        └──lib.rs
   │  │           └──26:    pub fn factorial_mult(&self, n: u32, #[callback_unwrap] cur: u32) -> u32 {
   │  ├──adder
   │  │  └──src
   │  │     └──lib.rs
   │  │        ├──30:        #[callback_unwrap] a: DoublePair,
   │  │        └──31:        #[callback_unwrap] b: DoublePair,
   │  └──callback-results
   │     └──src
   │        └──lib.rs
-> │           └──51:        #[callback_unwrap] a: u8,

Acceptance Criteria

Resources & Additional Notes

No response

Priority

🔴 P4 : Normal

[7-falseparfait]

Mind if I take this issue?

[TobieTom]

Hola Its Tobias. Im requesting for this task as requested

[dj8yfo]

@TobieTom you could also try take #1312, if the current one ends in a success