Improve PyMapping related function (#314)
* preliminary change
* pymapping get item
* validate_mapping
* fix for loop
* fix CI
* fix CI
* fix ci
* fix CI
* uncheck bounds
* mapping type
* dict error
* fix bad mapping tuple 1
* fix CI
* format code
* fix error test
* cargo clippy fix
* cargo clippy fix
* remove dead code
* fix import
* fix
* pypy has no PyTuple::get_item_unchecked
* fix lint
* rename func
* use get_item_unchecked
* not using unwrap
* iter mapping
* fix CI
* use macros
* fix dict iter
* simplify typeddict logic
* fix for pypy, small cleanup
* more test cases
Co-authored-by: Samuel Colvin <s@muelcolvin.com>
