48 chore refactor codebase and add developer documentation

[SizzleUnrlsd]

Context

This PR refactors the project architecture to move core logic out of main, improve maintainability, and add finer-grained module tests while preserving existing CLI behavior.

What Changed

• Orchestration refactor
  • Introduced AnalyzerApp as an application-layer orchestrator.
  • Introduced a reusable ArgParser (usable from CLI and library consumers).
  • Introduced modular analyzer components:
    • AnalysisPipeline
    • ModulePreparationService
    • DiagnosticEmitter
    • LocationResolver
• New analysis module
  • Added Reachability for classifying statically unreachable stack-access findings.
• main simplification
  • main.cpp now delegates to parser + app service.
• Logging cleanup
  • Migrated multiple analysis/pass traces to coretrace::logger for consistency.
• Library consumer example
  • Updated extern-project to demonstrate argument forwarding in library mode.
• Unit testing
  • Added fine-grained C++ module unit tests (stack_usage_analyzer_unit_tests) for:
    • LocationResolver
    • Reachability
    • ModulePreparationService
  • Unit-test binary is now opt-in via CMake:
    • -DBUILD_ANALYZER_UNIT_TESTS=ON
• run_test.py improvements
  • Expanded CLI option matrix coverage.
  • Added diagnostic rule coverage regression checks.
  • Integrated analyzer module unit-test execution when binary is present.
  • Graceful skip when unit-test binary is not built.
  • Excluded test/unit/* from integration fixture scans.
• Documentation
  • Added architecture doc for analyzer modules.
  • Updated root README (library-mode argument forwarding + architecture reference).
  • Added extern-project/README.
• CI
  • Added a consumer-fixture integration job validating JSON/SARIF outputs.

Architectural Rationale

This split enforces clear boundaries between:

• argument parsing/validation,
• application orchestration,
• analysis pipeline execution,
• diagnostic emission.

The result is lower coupling, better testability, and safer future evolution with reduced regression risk.

Compatibility

• CLI behavior remains functionally consistent.
• Analyzer module unit tests are now opt-in:
  • -DBUILD_ANALYZER_UNIT_TESTS=ON
• No expected breaking change for users consuming only the main analyzer binary.

Validation

• Main project build
• extern-project build
• Regression suite (run_test.py)
• Analyzer module unit tests: (when enabled)

Reviewer Notes

• Changes are split into atomic commits (CLI/app/main/analyzer/tests/docs/CI).
• Local untracked file analyse is intentionally excluded from this PR.

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coretrace-stack-analyzer found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.