Spell Flags Refactor

[walt253]

This PR refactors the spell flags logic and introduces a number of improvements:

• Custom Spells: It now supports custom Freeze, Heal, and Teleport spells. You can also truly combine multiple spell flags.

• Refactored AreaAffectType: No longer hardcoded to Slow or Disease. The introduced SpellEffect field allows Gas to inflict various statuses on enemies or allies that aren't immune.

• Spell Immunity: A new field in creature configuration files allows creatures to be immune to specific spell flags.

• SpellFlags Accept Names: SpellFlags now accept names rather than numbers, making it easier to understand and configure.

• Freeze Prisoners: No longer hardcoded to a specific instance. The freezer will now look for an appropriate instance that can freeze and use it.

• Disease Improvement: Disease now has a new feature where it can spread the last active spell that inflicted it. For example, combining Disease + Chicken will spread both statuses.

• Refactored Magic Use Powers: magic_use_power_heal, magic_use_power_timebomb, magic_use_power_chicken, and magic_use_power_disease have been merged into magic_use_power_apply_spell, which checks for immunities.

• Deprecated: IMMUNE_TO_GAS, UNAFFECTED_BY_WIND, IMMUNE_TO_DISEASE, and NEVER_CHICKENS are deprecated. However, they are still supported for backward compatibility in the NamedCommand and will work with config or script commands, but their flags have been removed. All configs in the project have been updated accordingly.

• Moved Flags: MagicFall and Grounded flags were removed from the spell flags. MagicFall is specifically for creature creation via the hero gate or summons, while Grounded is only used by Freeze against flying creatures. These flags have been moved to movement_flags.

This PR is large, so it will require thorough review and testing. I've tested the changes a bit, but the goal now is to identify any edge cases I might have missed or broken something else. I've left few comments on few parts of the code I've changed but I will add more to the PR itself to make it easier to review.