fix(ir): Add support for byte format in string validation

[k4n4ry]

Fixes #1261

Overview

I've added a new Byte field to the String structure in the validate package.
This field is set to true when format: byte is specified in the string formats of OpenAPI.
When executing character length validation, if the Byte field is true, the length is verified using []byte instead of []rune.

Note

This change may not be necessary.
According to the OpenAPI specification, format: byte is specified for base64-encoded characters.
If the characters used are those in base64 encoding, the length evaluation doesn't change during the []byte -> string -> []rune conversion process.
However, as mentioned in the issue, I suppose this change is necessary if we want to ensure validation behavior for more general bytes fields.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.93%. Comparing base (12fe015) to head (63919c9).
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1296      +/-   ##
==========================================
+ Coverage   73.92%   73.93%   +0.01%     
==========================================
  Files         189      189              
  Lines       12855    12860       +5     
==========================================
+ Hits         9503     9508       +5     
  Misses       2804     2804              
  Partials      548      548              

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