Refactor egs_sheets and ai_sheets into standalone libraries, remove preprocessor hacks

[Copilot]

The sheets_packer_shard tool couldn't build on Linux because EGS and AI sheets code was entangled with service globals via NO_EGS_VARS and NO_AI_COMP preprocessor guards. This refactors both into clean base classes usable by tools, with service-specific behavior in proper subclasses.

EGS sheets → ryzom_egs_sheets library

• Extracted egs_sheets/ into a standalone static library under ryzom/server/src/egs_sheets/
• Replaced extern CVariable<bool> references (LoadOutposts, EGSLight) with static setters on CSheets
• Replaced hardcoded IService::WriteFilesDirectory with CSheets::setWriteDirectory()
• Moved EGS-only method implementations (getBaseWeight, selectRandomLootSet, selectRandomCustomLootSet, QuarteringQuantityByVariable) to egs_sheets_egs_impl.cpp in EGS proper

AI sheets → base/subclass split

• Made CCreature::readGeorges()/serial() virtual, added onScriptComp() hook (no-op in base)
• CCreatureAI overrides onScriptComp() to create fight script comps via CFightScriptCompReader
• CSheetsAI overrides packSheets() to load CCreatureAI objects into the base _Sheets map
• Split ai_script_comp_base.h from ai_script_comp.h so sheets.h doesn't pull in CFightSelectFilter (which has vtable in ai_script_comp.cpp)

// Packer uses base classes directly — no script comp processing needed
AISHEETS::CSheets::getInstance()->packSheets(dir);

// AI service registers its subclass before init
AISHEETS::CSheetsAI::initInstance();
AISHEETS::CSheets::getInstance()->init();  // polymorphic, loads CCreatureAI

Build changes

• Removed WIN32 gate from sheets_packer_shard (now builds on Linux)
• Removed NO_EGS_VARS and NO_AI_COMP compile definitions entirely
• ryzom_egs_sheets library builds under WITH_RYZOM_TOOLS OR WITH_RYZOM_SERVER

Original prompt

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This section details on the original issue you should resolve

<issue_title>Refactor egs_sheets to separate library</issue_title>
<issue_description>Original report by Jan Boon (Bitbucket: [Jan Boon](https://bitbucket.org/Jan Boon), ).

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Refactor egs_sheets to seperate library for cleaner integration with shard sheets packer tool.

EGS sheets code does not crucially depend on EGS, so should be fairly easy.

There are several trivial dependencies to EGS caused by simple convenience functions which can easily be handled by giving the EGS itself a convenience subclass of the egs_sheets class.

Packed sheets write directory for init function should be passed as parameter preferably, instead of getting this from a function.
</issue_description>

<agent_instructions>We had trouble building the server sheet packing tool on Linux because of this, it's one of the remaining blockers that's keeping the whole gamedata pipeline from working on Linux :)</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@ryzom-pipeline **Original comment by Jan Boon (Bitbucket: [Jan Boon](https://bitbucket.org/Jan Boon), ).**

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The dependencies that need to be worked around are marked with NO_EGS_VARS

• Fixes Refactor egs_sheets to separate library #136

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