Cost and BV of superheavy meks

[SJuliez]

fixes MegaMek/megameklab#1523

• incorporate superheavy mek cost rules from IO:AE
• move arm actuator cost code to Mek to remove the duplicate code in BipedMek and TripodMek
• fix Tripods calculating leg actuator cost only for 2 legs
• consider structure costs of tripods
• consider the exact slots on superheavy meks for BV modifiers of explosive weapons (typically fewerthan on normal meks)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.02%. Comparing base (1d6c24b) to head (0d44a49).
Report is 50 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6557      +/-   ##
============================================
- Coverage     29.05%   29.02%   -0.04%     
+ Complexity    15160    15156       -4     
============================================
  Files          2835     2836       +1     
  Lines        279129   279271     +142     
  Branches      49214    49229      +15     
============================================
- Hits          81104    81058      -46     
- Misses       192652   192840     +188     
  Partials       5373     5373              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.