feat: flying enemies flee vertically, use preferred Z levels

[shmakota]

Purpose of change (The Why)

Suggested in the discord, and I've wanted to improve flying enemy support for a while.

Describe the solution (The How)

Allows flying enemies to flee upwards into the sky, and allows monsters to define a preferred Z level. Sunshine suggested a default of 3 for birds, which makes sense to me - preferrably zombie/aggro flying monsters should hover on 2, so they can use the hit and run style attacks if desired.

Describe alternatives you've considered

Testing

Additional context

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.