mem: reject blocks from other memory partitions

[Old-Ding]

Summary

• Reject blocks that are outside the target memory partition or are not aligned to its block size before adding them to the free list.
• Reuse OS_ERR_MEM_INVALID_P_BLK for invalid ownership and alignment.
• Keep the existing full-partition check and normal block return path unchanged.

Fixes #52.

Validation

• Built Source/os_mem.c with GCC 16.1.0 in the 32-bit POSIX/GNU CPU configuration using the official uC/CPU and uC/LIB headers (-fsyntax-only -Wall -Wextra -Werror).
• Ran a standalone host regression against the modified source with a 64-bit POSIX/GNU CPU configuration:
  • a block obtained from partition A is rejected when returned to partition B, and B's free-list head/count remain unchanged;
  • a non-block-start address from A is rejected;
  • the original block can still be returned to A successfully.
• git diff --check and git show --check passed.

The repository has no in-tree test framework, so the host regression harness is validation-only and is not included in the change.