builtin: fix m.clear() having different observable behavior to m = {}, after multiple iterations of setting keys and clearing (fix #22145)

[spytheman]

Fix #22145 .

[spytheman]

I've left this running locally:

import rand

const t = get_random_numbers()

fn get_random_numbers() []int {
	mut res := []int{}
	for i in 0..100 {
		res << rand.intn(1000) or { 0 }
	}
	return res
}

fn test_multiple_iterations_of_calling_clear_should_be_always_equivalent_to_assigning_a_new_map() {
	println('array t len: ${t.len}, t: ${t}')
	mut clr := map[int]int{}
	for i in 0 .. 0xFFFF {
		mut new := map[int]int{}
		clr.clear()
		for e in t {
			new[e] = e
			clr[e] = e
			assert new.len == clr.len // , 'mismatch found after setting element: $e, on iteration ${i}'
		}
		if i == 0 {
			dump(new.len)
			dump(new)
		}
		if i & 0x1FFF == 0 {
			println('index ${i}')
			// println('>> map     new: ${new.len} | ${new.keys().sorted()}')
			// println('>> map cleared: ${clr.len} | ${clr.keys().sorted()}')
		}
		assert new == clr // , 'mismatch found for iteration: ${i}'
	}
}

with this runner VFLAGS='-cc clang-18 -prod' ./run_randomised_test.sh:

#!/bin/bash

set -xe

while true; do
	date;
	v crun randomised_test.v ;
	sleep 0.1;
done

So far, it has not found other problems.

[spytheman]

The randomized test, found a counter example, that boils down to:

const t = [928, 897, 165, 563, 52, 619, 525, 414, 555, 254, 788, 8, 534, 0]

fn test_multiple_iterations_of_calling_clear_should_be_always_equivalent_to_assigning_a_new_map() {
    println('array t len: ${t.len}, t: ${t}')
    mut clr := map[int]int{}
    for i in 0 .. 0xFFFF {
        mut new := map[int]int{}
        clr.clear()
        for e in t {
            new[e] = e
            clr[e] = e
        }
        assert new == clr, 'mismatch found for iteration: ${i}'
    }
}

In it, const t = [928, 897, 165, 563, 52, 619, 525, 414, 555, 254, 788, 8, 534, 0] is interesting, since removing one of the elements, makes it pass. Changing some of the keys, like 165 to 65 or 0 to 1,2,3,4,5 also makes it pass, but other values can be changed and it still fails, for example 928 can become 28 or 897 -> 97 etc.