Range check for tower attacks is off by 8

[PiotrKaszuba]

Observations:

• a lot of range checks (one per creep I assume) when creeps out of range - would the same apply for every tower * every creep?

• when in range - checks are much more rare (when attack is ready). I get that it is known and optimized specifically for bonus round when towers almost always have attacks on cooldowns
• however, we get one check with 772 range - most likely missing +8 from RANGE_CHECK_BONUS_FOR_OTHER_UNITS

• same for this boss

• we get some checks that would allow the boss to be attacked (distance 777) range: 780 from code (tower.gd):
  var creeps_in_range: Array = Utils.get_units_in_range(self, _attack_target_type, get_position_wc3_2d(), attack_range)
• and other one that does not (distance 772) in tower.gd too:
  'var target_is_valid: bool = _target_is_valid(new_target)'

• and then checks get less frequent but still 780 and 772:

My initial idea would be to fix _target_is_valid in tower.gd by adding:
attack_range = Utils.apply_unit_range_extension(attack_range, _attack_target_type)

[Kvel2D]

From these notes, I mainly see that Tower._update_target_list() has a bug about RANGE_CHECK_BONUS_FOR_OTHER_UNITS.

1. It calls Utils.get_units_in_range() which adds RANGE_CHECK_BONUS_FOR_OTHER_UNITS
2. It also calls _target_is_valid() which does NOT add RANGE_CHECK_BONUS_FOR_OTHER_UNITS

I can confirm, current behavior is incorrect.

This fix is fine:

My initial idea would be to fix _target_is_valid in tower.gd by adding:
attack_range = Utils.apply_unit_range_extension(attack_range, _attack_target_type)