improve code quality

[ubogdan]

Describe the PR

• improve code quality
• clean some typos
• align structure data to use less memory

Relation issue
NONE

Additional context
NONE

[codecov]

Codecov Report

Merging #1047 (6d4346b) into master (5237c6d) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1047      +/-   ##
==========================================
+ Coverage   93.34%   93.46%   +0.11%     
==========================================
  Files           8        8              
  Lines        2134     2127       -7     
==========================================
- Hits         1992     1988       -4     
+ Misses         79       77       -2     
+ Partials       63       62       -1     

Impacted Files	Coverage Δ
swagger.go	100.00% <ø> (ø)
types.go	100.00% <ø> (ø)
field_parser.go	100.00% <100.00%> (+0.67%)	⬆️
gen/gen.go	95.68% <100.00%> (ø)
operation.go	95.00% <100.00%> (+0.03%)	⬆️
packages.go	76.83% <100.00%> (+0.04%)	⬆️
parser.go	92.26% <100.00%> (-0.01%)	⬇️
schema.go	100.00% <100.00%> (ø)

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[forsaken628]

typo

[ubogdan]

please comment on the code so I can fix it.