Pull request overview

This PR adds support for shrinking the program break (brk) by implementing logic to unmap pages when the heap shrinks. The implementation mirrors the existing expansion logic and ensures that only pages beyond the initially ELF-loaded heap region can be reclaimed.

Key changes:

• Added shrink logic that unmaps pages when the new break point is below the current heap top
• Protection of the initially mapped heap region (USER_HEAP_SIZE) from being unmapped

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