[#12301] Fix StackOverflowError with internal parent and CI-friendly revision

[gnodet]

Problem

When a multi-module project uses CI-friendly ${revision} with an internal parent in a subdirectory and a .mvn/ root marker, Maven 4 enters infinite recursion in DefaultModelBuilder:

readFileModel → getEnhancedProperties → doReadFileModel → cache → readFileModel → …

The cycle occurs because getEnhancedProperties() reads the root model to resolve CI-friendly properties, which triggers doReadFileModel() for the root POM, which calls getEnhancedProperties() again.

Fix

Added a shared Set<Path> activeModelReads to ModelBuilderSessionState that tracks which POM files are currently being read in an outer call frame. When getEnhancedProperties() detects that the root model is already being read (i.e., we're in a recursive call), it skips reading the root model to break the cycle.

The set is:

• Shared across all derived sessions (passed through derive())
• Thread-safe (ConcurrentHashMap.newKeySet())
• Self-cleaning (entries are removed in a finally block)

Integration Test

Added MavenITgh12301StackOverflowInternalParentRevisionTest with a reproducer project that has:

• A root POM with ${revision} and .mvn/ marker
• An internal parent module in a subdirectory

Fixes #12301

[github-actions]

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