Cluster artillery logic for when it doubles was poor

[TenkawaBC]

It only into account Fortified or woods, not additional terrain types (eg: rough, jungle).

I took the terrain types from the infantryInOpen check, removed the buildings and inversed it.

Added new report line so that cluster artillery reports when it doubled when not in the open.

This was done as per TO:AUE p. 166. This should fix issue #8086.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 29.90%. Comparing base (e6e0bc7) to head (334d386).
⚠️ Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
...amek/common/weapons/handlers/AreaEffectHelper.java	0.00%	8 Missing ⚠️
megamek/src/megamek/server/ServerHelper.java	0.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8150      +/-   ##
============================================
- Coverage     29.91%   29.90%   -0.01%     
+ Complexity    17380    17379       -1     
============================================
  Files          3172     3172              
  Lines        307484   307537      +53     
  Branches      53752    53774      +22     
============================================
- Hits          91990    91979      -11     
- Misses       205901   205974      +73     
+ Partials       9593     9584       -9     

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[Copilot]

Pull request overview

Updates artillery/infantry damage handling to better match TO:AUE p.166 by improving “in the open” determination and expanding cluster-munition doubling logic beyond just woods/fortified hexes.

Changes:

• Fix ServerHelper.infantryInOpen() logic around Urban Guerrilla + road/pavement so it only affects those terrain types.
• Update cluster-munition artillery damage to double against conventional infantry whenever they are not “in the open” (excluding buildings) and add a corresponding report line.
• Add a new report message string (ID 6046) for the new cluster-doubling report.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
megamek/src/megamek/server/ServerHelper.java	Corrects the Urban Guerrilla + pavement/road condition in the infantry “in open” check.
megamek/src/megamek/common/weapons/handlers/AreaEffectHelper.java	Replaces narrow terrain checks with a broader “not in open” check for cluster-munition doubling and emits a new report line.
megamek/resources/megamek/common/report-messages.properties	Adds report message 6046 used by the new report line.

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