`BuildHasher` is not completed when typing `RandomState::new().build_hasher`

[SludgePhD]

rust-analyzer version: 0.3.2482-standalone

rustc version: rustc 1.86.0 (05f9846f8 2025-03-31)

editor or extension: VSCode; v0.3.2482

relevant settings: none

code snippet to reproduce:

use std::hash::RandomState;

fn f() {
    RandomState::new().build_hasher
}

[ChayimFriedman2]

For context: this turned surprisingly tricky to do, see #t-compiler/rust-analyzer > Optimization causing funny bugs.