Merge branch 'main' into add_rustlings

PLANNING.md

book/book.toml

book/src/SUMMARY.md

book/src/cli.md

book/src/collections.md

book/src/lifetimes.md

book/src/part10.md

codes/rust_lang/collections/Cargo.toml

codes/rust_lang/collections/src/io.rs

codes/rust_lang/collections/src/lib.rs

codes/rust_lang/collections/src/main.rs

codes/rust_lang/collections/src/minimum.rs

codes/rust_lang/collections/src/something_or_nothing.rs

codes/rust_lang/lifetimes/Cargo.toml

codes/rust_lang/lifetimes/src/custom_int.rs

codes/rust_lang/lifetimes/src/io.rs

codes/rust_lang/lifetimes/src/lib.rs

codes/rust_lang/lifetimes/src/main.rs

codes/rust_lang/lifetimes/src/minimum.rs

codes/rust_lang/lifetimes/src/something_or_nothing.rs