feat(UI): show ammo per shot for weapons that use it

[chaosvolt]

Purpose of change (The Why)

Was suggested I make item UI tell the player when a gun uses more than one ammo per shot, just as it mentions UPS costs.

Describe the solution (The How)

In item.cpp, added a section to item::gun_info that checks if the gun's total ammo per shot is higher than one, and if so prints how many are used per shot.

Describe alternatives you've considered

Screaming.

Testing

1. Compiled and load-tested.
2. Spawned in a normal gun, saw it didn't show me ammo per shot info.
3. Spawned in a flamethrower, it shows 100 ammo per shot.
4. Installed a nozzle on it, it shows the value change.
5. Checked affected file for astyle.

Additional context

I also wanted to fix reasons-why-you-can't-fire messages printing multiple times when the gun has more than one fire mode but couldn't figure out how.

Checklist

Mandatory

• I wrote the PR title in conventional commit format.
• I ran the code formatter.
• I linked any relevant issues using github keyword syntax like closes #1234 in Summary of the PR so it can be closed automatically.
• I've committed my changes to new branch that isn't main so it won't cause conflict when updating main branch later.