make `shifted_in` and `shifted_out` const fns
make `shifted_in` and `shifted_out` const fns

Co-authored-by: csmoe <fcf1e72dff0420315a21b2eca780144689813ae4@users.noreply.github.com>

aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust