feat: improves escapeString's performance

[orisano]

fix #306

name           old time/op  new time/op  delta
306/stdjson-8   314µs ± 0%   312µs ± 1%   -0.61%  (p=0.000 n=10+8)
306/go-json-8  3.36ms ± 1%  0.12ms ± 0%  -96.50%  (p=0.000 n=10+8)

[codecov-commenter]

Codecov Report

Merging #345 (6f81106) into master (e99e62d) will decrease coverage by 0.00%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master     #345      +/-   ##
==========================================
- Coverage   79.87%   79.86%   -0.01%     
==========================================
  Files          52       52              
  Lines       17469    17496      +27     
==========================================
+ Hits        13953    13973      +20     
- Misses       2949     2955       +6     
- Partials      567      568       +1     

[goccy]

Thank you for contribution !!