fix: selector input unwanted readonly

[jeeanribeiro]

Summary

readonly prop should have an initial value of null or undefined, because svelte is adding the attribute in the HTML, and the HTML does not understand the readonly attribute with false or true value, just understand the absence of readonly prop

Changelog

- Sets the initial value of readonly prop in SelectorInput to null

Testing

Platforms

• Desktop
  • MacOS
  • Linux
  • Windows
• Mobile
  • iOS
  • Android

Checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented on my code, particularly in hard-to-understand areas
• I have added or modified tests that prove my changes work as intended
• I have verified that new and existing unit tests pass locally with my changes
• I have verified that my latest changes pass CI workflows for testing and linting
• I have made corresponding changes to the documentation

[Tuditi]

I added a commit to fix it also on NftInput and AssetAmountInput

[MarkNerdi996]

LGTM