test: add comprehensive unit tests for endpoint_builder module

[josecelano]

Description

This PR adds comprehensive unit tests for the endpoint_builder module in the application layer's common command handlers.

Changes

• Added 16 unit tests covering all three public functions:
  • build_api_endpoint() - 5 tests
  • build_http_tracker_endpoint() - 5 tests
  • build_all_tracker_endpoints() - 6 tests

Test Coverage

The tests cover:

• ✅ HTTP endpoint building (without TLS)
• ✅ HTTPS endpoint building (with TLS)
• ✅ Correct path handling (/api/health_check vs /health_check)
• ✅ Port extraction from configuration
• ✅ Instance IP usage and propagation
• ✅ Multiple tracker endpoint building
• ✅ Empty tracker list handling
• ✅ Port configuration preservation

Testing Approach

Following the project's unit testing conventions:

• Tests are in the same file using #[cfg(test)] mod tests { ... }
• Using behavior-driven naming: it_should_{behavior}_when_{condition}
• Pure unit tests with no external dependencies beyond domain types

Pre-commit Checks

All pre-commit checks pass:

• ✅ Cargo machete (no unused dependencies)
• ✅ Markdown linting
• ✅ YAML linting
• ✅ TOML linting
• ✅ Spell checking
• ✅ Clippy (all warnings fixed)
• ✅ Rustfmt
• ✅ ShellCheck
• ✅ All tests pass (16/16 new tests + existing test suite)

[josecelano]

ACK d61aaf5

[josecelano]

ACK 7621c1e