refactor: use slices.Contains to simplify code

[hardlydearly]

There is a new function added in the go1.21 standard library, which can make the code more concise and easy to read.

[KaloyanTanev]

@hardlydearly can you format your PR description, according to the guidelines?

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[hardlydearly]

@hardlydearly can you format your PR description, according to the guidelines?

Done. Please review again.

[KaloyanTanev]

@hardlydearly Please read the contributing.md doc here.

[pinebit]

@hardlydearly Please read the contributing.md doc here.

And also this section: https://github.com/ObolNetwork/charon/blob/main/docs/contributing.md#chore-prs

[hardlydearly]

@hardlydearly Please read the contributing.md doc here.

And also this section: https://github.com/ObolNetwork/charon/blob/main/docs/contributing.md#chore-prs

Thanks. Modified. Please review again.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 53.67%. Comparing base (0246897) to head (71bc5e9). Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3668      +/-   ##
==========================================
- Coverage   53.72%   53.67%   -0.05%     
==========================================
  Files         223      223              
  Lines       35379    35379              
==========================================
- Hits        19008    18991      -17     
- Misses      14264    14283      +19     
+ Partials     2107     2105       -2     

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