fix(comp:radio): gap behaves abnormally when configured without 0px

[threedayAAAAA]

fix #1684

PR Checklist

Please check if your PR fulfills the following requirements:

• [-] The commit message follows our guidelines
• [-] Tests for the changes have been added/updated or not needed
• [-] Docs and demo have been added/updated or not needed

What is the current behavior?

IxRadioGroup的gap配置，对字符串和数字的处理不一致

What is the new behavior?

IxRadioGroup的gap配置为0px时与配置为0表现一致

Other information

[idux-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3692447) 92.31% compared to head (b635e42) 92.31%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1740   +/-   ##
=======================================
  Coverage   92.31%   92.31%           
=======================================
  Files         346      346           
  Lines       32786    32786           
  Branches     3709     3709           
=======================================
  Hits        30268    30268           
  Misses       2518     2518           

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