Simplify Twig templates with pre-computed values

[dereuromark]

Summary

Introduces TemplateDataPreparer class that moves conditional logic from Twig templates into PHP for better maintainability and testability.

Key principle: Only extract logic that computes flags/values - no PHP code generation inside PHP.

Pre-computed values

DTO-level:

• needsInvalidArgumentException - true if any field is required
• needsRuntimeException - true if any field is nullable or has associative singular

Field-level flags:

• useWithMethod - use with* methods (immutable DTOs)
• needsOrFailMethod - generate *OrFail variants (nullable fields)
• needsHasMethod - generate has* method
• useImmutableCollectionMethods - withAdded/withRemoved
• useMutableCollectionMethods - add/remove

Property declaration:

• propertyVisibility - 'protected' or 'public readonly'
• propertyTypeHint - computed type hint
• propertyDefault - default value string

Templates simplified

Template	Before	After
dto.twig	7-line loop to detect exceptions	Uses pre-computed flags
methods.twig	Dense single-line conditionals	Readable flag checks with comments
property.twig	300+ char line with nested conditionals	Uses pre-computed values

What we intentionally kept in Twig

• Lazy loading hydration code in method_get.twig - kept as template conditionals to avoid generating PHP inside PHP

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.09%. Comparing base (0476c67) to head (8f70c5d).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Generator/TemplateDataPreparer.php	80.95%	12 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #100      +/-   ##
============================================
- Coverage     83.11%   83.09%   -0.03%     
- Complexity     1415     1447      +32     
============================================
  Files            41       42       +1     
  Lines          3477     3543      +66     
============================================
+ Hits           2890     2944      +54     
- Misses          587      599      +12     

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