refactor: replace Split in loops with more efficient SplitSeq

[slightsharp]

Description

strings.SplitSeq (introduced in Go 1.23) returns a lazy sequence (strings.Seq), allowing gopher to iterate over tokens one by one without creating an intermediate slice.

It significantly reduces memory allocations and can improve performance for long strings.

More info: golang/go#61901

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Author Checklist

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I have...

• tackled an existing issue or discussed with a team member
• left instructions on how to review the changes
• targeted the main branch

[aljo242]

Is this function tested?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.61%. Comparing base (d77f482) to head (7ecf764).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #945      +/-   ##
==========================================
+ Coverage   64.77%   65.61%   +0.83%     
==========================================
  Files         318      318              
  Lines       22292    22204      -88     
==========================================
+ Hits        14440    14569     +129     
+ Misses       6566     6477      -89     
+ Partials     1286     1158     -128     

Files with missing lines	Coverage Δ
ethereum/eip712/types.go	92.74% <100.00%> (ø)

... and 7 files with indirect coverage changes

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