Some changes mostly polish and C++ safety

[justinhj]

Summary

Pre-release hardening, robustness enhancements, and CI checks for the **v1.4.2** release.

### Key Changes

1. **Rule of 3/5 Copy Prevention (`stlastar.h`, `fsa.h`)**
   - Explicitly deleted copy constructor and copy assignment operator (`= delete`) on both `AStarSearch` and

FixedSizeAllocator.
- Prevents accidental pass-by-value shallow copying of internal raw pointers (m_pMemory, m_Start, m_Goal),
which previously led to double-free crashes on scope exit.

2. **Search Reuse Safety (`stlastar.h`)**
   - In `SetStartAndGoalStates()`, added an automatic cleanup check: if `m_Start != nullptr`, any prior search nodes

are freed before allocating start and goal nodes for the new search.
- Eliminates node leaks when an existing AStarSearch instance is reused without manual calls to
FreeSolutionNodes().

3. **Allocator Underflow Protection (`fsa.h`)**
   - Added an assertion and early exit guard for `MaxElements == 0` to prevent `m_MaxElements - 1` unsigned underflow

in the free-list initialization loop.

4. **Universal Leak Assertion (`stlastar.h`)**
   - Removed the `#if USE_FSA_MEMORY` preprocessor guard from `EnsureMemoryFreed()`.
   - Node allocation balance (`assert(m_AllocateNodeCount == 0)`) is now actively validated in both pool-allocated and

standard heap (#define USE_FSA_MEMORY 0) configurations.

5. **CI Workflow Verification (`.github/workflows/c-cpp.yml`)**
   - Added a `Run Examples` step running `./findpath`, `./minpathbucharest`, and `./8puzzle 013824765` to verify all

sample executables build and run cleanly on every push and PR.

6. **Benchmark Tuning (`bench.cpp`)**
   - Set `NUM_SEARCHES` to 20,000 for practical benchmark runtimes.

7. **Unit Tests (`tests.cpp`)**
   - Added `SetStartAndGoalStates Cleans Up Previous Search On Reuse` to verify leak-free instance reuse.
   - Added `AStarSearch and FixedSizeAllocator Are Non-Copyable` using `<type_traits>` to enforce non-copyability at

compile time.

### Testing
- All 9 unit tests pass cleanly (`ctest --test-dir build --output-on-failure`).
- Verified all example executables run and exit with code 0.