Zupt v2.1.2: add full-disk backup/restore, expand test suite, improve compression handling

- Introduced full-disk backup/restore (src/zupt_disk.c, ~530 LOC)
  - Backup: streams 4MB blocks with sparse detection and all codecs
  - Restore: per-block checksum validation for integrity
  - Supports password (-p), PQ hybrid (--pq), or no encryption
  - Real-time progress bar with throughput reporting (stderr)

- Implemented sparse detection (8-byte zero scan)
  - Zero blocks stored as STORE (near-zero overhead)

- Added disk-aware safeguards
  - ZUPT_FLAG_DISK_IMAGE prevents misuse with extract
  - Immediate failure on wrong password during first block decrypt

- Cross-platform device size detection
  - Linux: BLKGETSIZE64
  - macOS: DKIOCGETBLOCKCOUNT
  - Fallback: lseek

- Compression behavior
  - ~2928:1 on highly repetitive data
  - ~1.33:1 on random data (auto STORE fallback)

- Expanded test suite to 77 tests:
  - 11 VV unit
  - 13 NIST/RFC vectors
  - 22 regression
  - 14 multi-threaded
  - 10 post-quantum
  - 7 disk (normal, encrypted, PQ, sparse, LZHP, extreme compression, wrong-password)

Release stats:
- 74 files, 168KB, zero .o artifacts
- 77/77 tests passing
- Fully clean under ASAN + UBSan

Makefile

@@ -50,7 +50,7 @@ ZUPT_SOURCES = src/zupt_main.c src/zupt_format.c src/zupt_lz.c src/zupt_lzh.c \
                src/zupt_xxh.c src/zupt_sha256.c src/zupt_aes256.c src/zupt_crypto.c \
                src/zupt_predict.c src/zupt_parallel.c src/zupt_keccak.c \
                src/zupt_x25519.c src/zupt_mlkem.c src/zupt_cpuid.c src/zupt_mlock.c \
-               src/zupt_filetype.c
+               src/zupt_filetype.c src/zupt_disk.c
 
 # --- VAPTVUPT: VaptVupt codec sources (Apache-2.0, integrated under MIT) ---
 VV_SOURCES = src/vv_encoder.c src/vv_decoder.c src/vv_ans.c \