…nary size

This is a complete rewrite that eliminates all std dependencies and heap allocations:
- Converted from std to no_std with custom C entry point (main) and panic handler
- Replaced std::fs and PathBuf with direct libc calls (getcwd, stat, strlen)
- All operations now use stack-allocated buffers (4096 byte arrays)
- Added comprehensive error handling for edge cases (empty paths, buffer overflow)

The implementation now directly interfaces with libc:
- Uses getcwd() for current directory instead of env::current_dir()
- Uses stat() syscall to check file existence instead of Path::exists()
- Manual path string manipulation with byte slices instead of PathBuf
- Zero-copy argument parsing from argv

Added rust_eh_personality() symbol to satisfy DWARF debug info references in libcore
that appear with panic=abort in recent Rust versions. This empty function is never
actually called at runtime but prevents linker errors.

Added extensive test suite with 24 unit tests covering:
- Path traversal logic (find_parent edge cases)
- Buffer safety (overflow handling, PATH_MAX limits)
- C string operations (strlen with various inputs)
- File existence checking with Miri-compatible mocks

Cargo.toml changes:
- Added libc dependency with default-features = false
- Enhanced release profile for maximum size optimization