Fix warnings about positional parameter mismatch

[straight-shoota]

Implementations of abstract methods should use the same parameter names as the abstract def.

This patch fixes that and removes the respective warnings:

In structural/flyweight.cr:26:15

 26 | def draw_at(_pos : Position)
                  ^---
Warning: positional parameter '_pos' corresponds to parameter 'pos' of the overridden method FlyweightTree#draw_at(pos : Position), which has a different name and may affect named argument passing

A total of 1 warnings were found.

In behavioral/interpreter.cr:63:16

 63 | def evaluate(_press)
                   ^-----
Warning: positional parameter '_press' corresponds to parameter 'press' of the overridden method Evaluator#evaluate(press), which has a different name and may affect named argument passing

A total of 1 warnings were found.

In behavioral/mediator.cr:55:26

 55 | def perform_move(move, fighter)
                             ^------
Warning: positional parameter 'fighter' corresponds to parameter 'performer' of the overridden method MediatorBase#perform_move(move, performer), which has a different name and may affect named argument passing

A total of 1 warnings were found.

In behavioral/strategy.cr:38:14

 38 | def attack(ft, op)
                 ^-
Warning: positional parameter 'ft' corresponds to parameter 'fighter' of the overridden method FightStrategy#attack(fighter, opponent), which has a different name and may affect named argument passing

In behavioral/strategy.cr:38:18

 38 | def attack(ft, op)
                     ^-
Warning: positional parameter 'op' corresponds to parameter 'opponent' of the overridden method FightStrategy#attack(fighter, opponent), which has a different name and may affect named argument passing

In behavioral/strategy.cr:45:14

 45 | def attack(ft, op)
                 ^-
Warning: positional parameter 'ft' corresponds to parameter 'fighter' of the overridden method FightStrategy#attack(fighter, opponent), which has a different name and may affect named argument passing

In behavioral/strategy.cr:45:18

 45 | def attack(ft, op)
                     ^-
Warning: positional parameter 'op' corresponds to parameter 'opponent' of the overridden method FightStrategy#attack(fighter, opponent), which has a different name and may affect named argument passing

A total of 4 warnings were found.

[veelenga]

Thank you 🙏