Explicit tail calls are now available on Rust Nightly (become keyword)

Link to actual GitHub PR since Reddit blocks some ASNs: https://github.com/rust-lang/rust/pull/144232

From documentation, and a test in the PR:

    When tail calling a function, instead of its stack frame being added to the
    stack, the stack frame of the caller is directly replaced with the callee's.
    This means that as long as a loop in a call graph only uses tail calls, the
    stack growth will be bounded.

    This is useful for writing functional-style code (since it prevent recursion
    from exhausting resources) or for code optimization (since a tail call
    *might* be cheaper than a normal call, tail calls can be used in a similar
    manner to computed goto).

    pub fn fibonacci(n: u64, a: u64, b: u64) -> u64 {
        match n {
            0 => a,
            1 => b,
            _ => become fibonacci(n - 1, b, a + b),
        }
    }

See also: https://docs.rs/tailcall