Character variants dont working
I tried few [character variants of iosevka font](https://github.com/be5invis/Iosevka/blob/main/doc/character-variants.md)
all of them are working fine in default iosevka font
and no one is working with iosevka nerd font

font features with boolean value works fine, bug is about character variants.

```
<edit name="fontfeatures" mode="append">
  <string>ss12 on</string>
  <string>cv10 2</string>
  <string>cv06 1</string>
  <string>cv19 2</string>
  <string>cv09 1</string>
</edit>

```
expected: all settings applied
happen: only ss12 applied

### Example Symbols or Text

https://github.com/be5invis/Iosevka/blob/main/doc/character-variants.md

### Font Used

IosevkaTerm Nerd Font Mono

### Source of Font File

Nixpkgs unstable. nerd-fonts.iosevka-term

### Terminal Emulator (and the title of the terminal window)

foot

### Operating System and Version

NixOS 25.05 (Warbler) x86_64