Fix: critical malloc size calculation bug

Summary:
- Fixed an integer arithmetic error in malloc() where 'nunits' was initialized to 0, causing incorrect heap sizing.
- This bug caused malloc to return pointers pointing to unmapped memory pages, leading to Store Page Fault (scause 15) at process boundaries.
- Switched memory allocator logic to use byte-based size calculation instead of K&R style units to prevent off-by-one errors.

Improvements:
- Shell now starts successfully without segfaults.

5 files changed, 0 insertions, 0 deletions

diff --git a/build/src/kernel/initcode.o b/build/src/kernel/initcode.o
index c575853..cb2dd53 100644
--- a/build/src/kernel/initcode.o
+++ b/build/src/kernel/initcode.o
diff --git a/build/src/kernel/mm/vm.o b/build/src/kernel/mm/vm.o
index d73e9a6..96840aa 100644
--- a/build/src/kernel/mm/vm.o
+++ b/build/src/kernel/mm/vm.o
diff --git a/build/src/kernel/proc/exec.o b/build/src/kernel/proc/exec.o
index 5b735ed..26a77b6 100644
--- a/build/src/kernel/proc/exec.o
+++ b/build/src/kernel/proc/exec.o
diff --git a/build/src/kernel/proc/proc.o b/build/src/kernel/proc/proc.o
index 7ae741b..940c575 100644
--- a/build/src/kernel/proc/proc.o
+++ b/build/src/kernel/proc/proc.o
diff --git a/build/src/kernel/trap/handler.o b/build/src/kernel/trap/handler.o
index 44a2baa..bd42409 100644
--- a/build/src/kernel/trap/handler.o
+++ b/build/src/kernel/trap/handler.o