[MNG-8653] Fix 'all' phase and add 'each' phase

[gnodet]

JIRA issue: MNG-8653

Fixes the existing 'all' phase and introduces a new 'each' phase to better support
hierarchical builds and concurrent execution:

• 'all': Properly coordinates execution across parent-child project hierarchies
• 'each': A new phase that executes for each individual project in isolation

Key changes:

• Enhanced BuildPlanExecutor to properly handle parent-child relationships in phases
• Added new children() pointer type for explicit phase dependencies
• Improved phase dependency management to ensure:
  • Parent's before:all executes before children's phases
  • Children's after:all executes before parent's after:all
  • Each project's phases execute in isolation within the 'each' phase
• Added comprehensive documentation to BuildPlanExecutor
• Added integration test to verify hierarchical phase execution

This commit also fixes thread-safety issues in concurrent builds:

• Added synchronization to ReactorReader for project operations
• Improved thread-safety for project-level clean and install operations
• Enhanced build step state management in concurrent scenarios

Fixes: MNG-8653

[jira-importer]

Resolve #9658