TinyUfo: evict race condition updating weights

[RichardBsolut]

Describe the bug

An race condition exists while updating weights. Where one thread pushes an small Item while an concurrent thread evict that item before weight's added. Leading to an USize underflow which leads to add with overflow in evict_to_limit.

TinyUfo info

TinyUfo: 0.6.0
Rust version: cargo 1.91.1 (ea2d97820 2025-10-10)
Operating system version: Debian 12.4

Steps to reproduce

use tinyufo::TinyUfo;
use std::sync::Arc;

fn explode(id: usize, ufo: Arc<TinyUfo<String, String>>) {
    let keys =(0..5).map(|keyid|format!("{}_{}", id, keyid)).collect::<Vec<_>>();
    let cnt = 0;
    loop {
        let value = format!("V_{}", cnt);
        for key in &keys {
            ufo.put(key.clone(), value.clone(), 1);
            ufo.get(key); ufo.get(key);
        }
    }
}

fn main() {
    let tufo = Arc::new(TinyUfo::<String, String>::new(5, 5));
    for n in 0..100 {
        let myufo = tufo.clone();
        let thread = std::thread::spawn(move || {
            explode(n, myufo)
        });
        if n == 99 {
            let _ = thread.join();
        };
    }
}

Observed results

thread '<unnamed>' (2692814) panicked at tinyufo/src/lib.rs:248:15:
attempt to add with overflow
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/07bdbaedc63094281483c40a88a1a8f2f8ffadc5/library/std/src/panicking.rs:690:5
   1: core::panicking::panic_fmt
             at /rustc/07bdbaedc63094281483c40a88a1a8f2f8ffadc5/library/core/src/panicking.rs:80:14
   2: core::panicking::panic_const::panic_const_add_overflow
             at /rustc/07bdbaedc63094281483c40a88a1a8f2f8ffadc5/library/core/src/panicking.rs:175:17
   3: tinyufo::FiFoQueues<T>::evict_to_limit
             at /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/TinyUFO-0.6.0/src/lib.rs:255:15
   4: tinyufo::FiFoQueues<T>::admit
             at /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/TinyUFO-0.6.0/src/lib.rs:189:40
   5: tinyufo::TinyUfo<K,T>::put
             at /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/TinyUFO-0.6.0/src/lib.rs:424:21

[RichardBsolut]

Linking the proposed fix: PR #769