minor refactor to signing method

[Fraccaman]

Describe your changes

Minor refactor to how signing data is fetched.

Indicate on which release or other PRs this topic is based on

Checklist before merging to draft

• I have added a changelog
• Git history is in acceptable state

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 70 lines in your changes missing coverage. Please review.

Project coverage is 54.54%. Comparing base (7b052e5) to head (87e939e).
Report is 3 commits behind head on main.

Files	Patch %	Lines
crates/sdk/src/tx.rs	0.00%	58 Missing ⚠️
crates/sdk/src/signing.rs	0.00%	9 Missing ⚠️
crates/apps_lib/src/client/tx.rs	0.00%	2 Missing ⚠️
crates/sdk/src/eth_bridge/bridge_pool.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3592      +/-   ##
==========================================
- Coverage   54.55%   54.54%   -0.02%     
==========================================
  Files         323      323              
  Lines      113871   113888      +17     
==========================================
- Hits        62118    62115       -3     
- Misses      51753    51773      +20     

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