Zombie Improvements

This mod improves zombie leader and reinforcement mechanics and fixes a few bugs with them.

What?

If you didn't even know these were a thing, here's a rundown from the Minecraft wiki:

On all difficulty levels, damaged zombie mobs (including husks, drowned and even zombified piglins) call all other zombies within a 67×21×67 to 111×21×111 area centered on the attacked zombie to target the attacker.

In Hard difficulty, zombies can spawn additional zombies to "help" when damaged. Each zombie has a "likeliness to call reinforcements" statistic ranging from 0–10%, and "leader" zombies (0–5% depending on regional difficulty) get a bonus of 50–75 percentage points to the stat.

On Hard difficulty, zombies have a 5% chance to spawn as leaders. Leader zombies can spawn other zombies as reinforcements.

So what does this mod do?

There are a few issues with these mechanics:

You can't tell if the zombie you're attacking is a leader or not.
There is no visual/audio cue when zombies spawn additional reinforcements.
There are a few bugs which make these mechanics less relevant.

This mod alleviates all of these issues by:

Adding a red aura effect around leader zombies, identical to the charged creeper effect, but red color.
Adding unique textures and sounds for leader zombies.
Increasing the size of zombies that are leaders.
Adding a sound that plays when a zombie spawns in additional reinforcements. The sound that will be played is the block breaking sound of the block the freshly spawned zombie is standing on, played 5 times in a span of 2 seconds.
Appending a "Leader" prefix to the name of the leader mob.
Fixing two vanilla bugs, namely MC-219981 and (1.21.1 only) MC-14800.

There's also a few additional tweaks:

Configure the attack damage of leader zombies. By default, it's slightly increased compared to normal zombies.
Configure the spawn chance for leader zombies.
Allow only leader zombies to spawn additional reinforcements.
Prevent mob spawners from spawning leaders.
Prevent zombies spawned by mob spawners from spawning additional reinforcements.