[stdlib] fix: remove DictEntry.__copyinit__ in Dict methods (Pointer, speed up)

[rd4com]

Hello, this probably fixes some bug reports 🥳
it is also now faster because we use Pointer and it removes __copyinit__

Many methods like __getitem__ uses _find_index,
it was doing __copyinit__ on entries while iterating

The result is also a speedup, especially on types that allocate memory,
best speedup is probably for V:Arc 👍

It should also speedup **kwargs!

[rd4com]

🔥 benchmarks

Theses are some small simple benchmarks with Time.now(),
speedups increases with the size of the dictionary ❤️‍🔥

690781 3264000 (1.13x)
885908 6528000 (1.19x)
2173504 6593800 (3.36x)
1645963 6659600 (2.32x)
316705 6725400 (7.3x)

from time import now
from collections import Dict

alias iteration_size = 1<<8
def main():
    var result: Int=0
    var start = now()
    var stop = now()

    
    small = Dict[Int, Int]()
    start = now()
    for x in range(100):
        for i in range(iteration_size):
            small[i]=i
        for i in range(iteration_size): 
            result += small.pop(i)
    stop = now()
    print(stop-start, result)
    
    start = now()
    for x in range(100):
        small = Dict[Int, Int]()
        for i in range(iteration_size):
            small[i]=i
        for i in range(iteration_size): 
            result += small[i]
    stop = now()
    print(stop-start, result)
    
    start = now()
    for x in range(100):
        small2 = Dict[Int, String]()
        @parameter
        for i in range(iteration_size):
            alias tmp = str(i)
            small2[i]=tmp
        for i in range(iteration_size): 
            result += len(small2[i])
    stop = now()
    print(stop-start, result)
    
    small2 = Dict[Int, String]()
    start = now()
    for x in range(100):
        @parameter
        for i in range(iteration_size):
            alias tmp = str(i)
            small2[i]=tmp
        for i in range(iteration_size): 
            result += len(small2.pop(i))
    stop = now()
    print(stop-start, result)
    
    small2 = Dict[Int, String]()
    @parameter
    for i in range(iteration_size):
        alias tmp = str(i)
        small2[i]=tmp
    start = now()
    for x in range(100):
        for i in range(iteration_size): 
            result += len(small2[i])
    stop = now()
    print(stop-start, result)