Fix slab size when resetting mutable storable in Array

[fxamacker]

Updates #292 #335

Changes

Recompute slab size by adding all element sizes instead of using the size diff of old
and new element because oldElem can be the same storable when the same value is reset
and oldElem.ByteSize() can equal storable.ByteSize().

Given this, size diff of the old and new element can be 0 even when its actual size changed.

This is prep work for atree inlining to prevent a bug from surfacing.

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[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.08% 🎉

Comparison is base (74e19aa) 65.24% compared to head (dda0495) 65.32%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #336      +/-   ##
==========================================
+ Coverage   65.24%   65.32%   +0.08%     
==========================================
  Files          14       14              
  Lines        8761     8773      +12     
==========================================
+ Hits         5716     5731      +15     
+ Misses       2327     2325       -2     
+ Partials      718      717       -1     

Files Changed	Coverage Δ
array.go	70.69% <100.00%> (+0.15%)	⬆️

... and 1 file with indirect coverage changes

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[ramtinms]

looks good to me, Just to confirm my understanding this only iterates over the size of values of the current slab and nothing beyond that? if for example we have an array with many underlying slabs, changes in one element doesn't require the whole array to go and scan all the slabs ?

[fxamacker]

@ramtinms

looks good to me, Just to confirm my understanding this only iterates over the size of values of the current slab and nothing beyond that? if for example we have an array with many underlying slabs, changes in one element doesn't require the whole array to go and scan all the slabs ?

Yes, this only iterates over the sizes of elements in current slab. It doesn't require scanning of the whole array.