Allow testing of HolidayDatabase-related functions (and add relevant tests to Modifiers)

[gausie]

No description provided.

[codecov]

Codecov Report

Merging #564 (6f4e5bd) into main (7c6f78a) will increase coverage by 0.05%.
The diff coverage is 84.21%.

@@             Coverage Diff              @@
##               main     #564      +/-   ##
============================================
+ Coverage     20.36%   20.41%   +0.05%     
- Complexity     8584     8613      +29     
============================================
  Files           998      998              
  Lines        155995   155995              
  Branches      34704    34703       -1     
============================================
+ Hits          31768    31847      +79     
+ Misses       118307   118222      -85     
- Partials       5920     5926       +6     

Impacted Files	Coverage Δ
...rceforge/kolmafia/persistence/HolidayDatabase.java	35.07% <78.57%> (+4.78%)	⬆️
src/net/sourceforge/kolmafia/Expression.java	89.51% <100.00%> (+1.60%)	⬆️
...sourceforge/kolmafia/textui/langserver/Script.java	81.91% <0.00%> (-3.20%)	⬇️
src/net/sourceforge/kolmafia/RequestLogger.java	9.83% <0.00%> (+1.16%)	⬆️
...urceforge/kolmafia/swingui/menu/ScriptMRUList.java	52.11% <0.00%> (+1.40%)	⬆️
src/net/sourceforge/kolmafia/StaticEntity.java	20.39% <0.00%> (+4.46%)	⬆️
.../net/sourceforge/kolmafia/utilities/LogStream.java	79.16% <0.00%> (+64.58%)	⬆️

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