fix(katana-core): dont use optional dep in non-feature specific code

[kariy]

before this, running cargo test -p katana-core would result in error bcs we're using ethers crate in non-feature code

ref #1527

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.01%. Comparing base (48e7261) to head (8d0f6ca).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1746      +/-   ##
==========================================
- Coverage   68.69%   68.01%   -0.68%     
==========================================
  Files         296      304       +8     
  Lines       32342    32912     +570     
==========================================
+ Hits        22218    22386     +168     
- Misses      10124    10526     +402     

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