Fix assign nil slice value

[goccy]

fix #275 ( also fix #268 )

If you decode using the same variable multiple times, the pointer from the previous decoding remains.
At this time, for example, the slice size is 32bytes in a 64-bit environment, so if library initialize only the start address with nil, the latter 24 bytes will remain with invalid values. To avoid this, I tried to initialize all fields by typedmemmove .

[codecov-commenter]

Codecov Report

Merging #276 (bf35de8) into master (14f03c1) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #276      +/-   ##
==========================================
+ Coverage   81.33%   81.34%   +0.01%     
==========================================
  Files          47       47              
  Lines       15516    15516              
==========================================
+ Hits        12620    12622       +2     
+ Misses       2336     2335       -1     
+ Partials      560      559       -1