Backend unit tests: (mld_polyz_unpack/_c)

[willieyz]

• Related Backend unit tests #777
• During Backend unit tests #777 , we found some potential problem with unit test for mld_polyz_unpack, we open this PR for tracking and investigation.
• Error log

=================================================================
  ==19858==ERROR: AddressSanitizer: unknown-crash on address 0x7ffff4b0024e at pc 0x000000418234 bp 0x7fffffffaa30 sp 0x7fffffffaa28
  READ of size 32 at 0x7ffff4b0024e thread T0
      #0 0x418233 in PQCP_MLDSA_NATIVE_MLDSA44_mld_polyz_unpack_17_avx2 (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x418233)
      #1 0x4108c3 in PQCP_MLDSA_NATIVE_MLDSA44_polyz_unpack (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x4108c3)
      #2 0x403671 in test_mld_polyz_unpack_core (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x403671)
      #3 0x403ba8 in test_native_polyz_unpack (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x403ba8)
      #4 0x402b15 in main (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x402b15)
      #5 0x7ffff6c2a47d in __libc_start_call_main (/nix/store/2j5v2nxxkqd6i53bzrg594rrr5r2v95b-glibc-join/lib/libc.so.6+0x2a47d) (BuildId: 184c6644327611cadef0a544327ebb842fceaa2c)
      #6 0x7ffff6c2a538 in __libc_start_main_alias_1 (/nix/store/2j5v2nxxkqd6i53bzrg594rrr5r2v95b-glibc-join/lib/libc.so.6+0x2a538) (BuildId: 184c6644327611cadef0a544327ebb842fceaa2c)
      #7 0x402f44 in _start (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x402f44)
  
  Address 0x7ffff4b0024e is located in stack of thread T0 at offset 590 in frame
      #0 0x403aef in test_native_polyz_unpack (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x403aef)
  
    This frame has 1 object(s):
      [32, 608) 'test_bytes' (line 476) <== Memory access at offset 590 partially overflows this variable
  HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
        (longjmp and C++ exceptions *are* supported)
  SUMMARY: AddressSanitizer: unknown-crash (/home/runner/work/mldsa-native/mldsa-native/test/build/mldsa44/bin/test_unit44+0x418233) in PQCP_MLDSA_NATIVE_MLDSA44_mld_polyz_unpack_17_avx2
  Shadow bytes around the buggy address:
    0x7ffff4afff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0x7ffff4b00000: f1 f1 f1 f1 00 00 00 00 00 00 00 00 00 00 00 00
    0x7ffff4b00080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0x7ffff4b00100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0x7ffff4b00180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  =>0x7ffff4b00200: 00 00 00 00 00 00 00 00 00[00]00 00 f3 f3 f3 f3
    0x7ffff4b00280: f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 00 00 00 00
    0x7ffff4b00300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0x7ffff4b00380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0x7ffff4b00400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0x7ffff4b00480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  Shadow byte legend (one shadow byte represents 8 application bytes):
    Addressable:           00
    Partially addressable: 01 02 03 04 05 06 07 
    Heap left redzone:       fa
    Freed heap region:       fd
    Stack left redzone:      f1
    Stack mid redzone:       f2
    Stack right redzone:     f3
    Stack after return:      f5
    Stack use after scope:   f8
    Global redzone:          f9
    Global init order:       f6
    Poisoned by user:        f7
    Container overflow:      fc
    Array cookie:            ac
    Intra object redzone:    bb
    ASan internal:           fe
    Left alloca redzone:     ca
    Right alloca redzone:    cb
  ==19858==ABORTING
  make: *** [Makefile:72: run_unit_44] Error 1

[hanno-becker]

We should be able to pick this up now that #784 is merged?