feat: Signer trait for RevmMiddleware

[Autoparallel]

Give an overview of the tasks completed
Implements the Signer trait for the RevmMiddleware struct.

[codecov]

Codecov Report

Attention: 60 lines in your changes are missing coverage. Please review.

Comparison is base (a6744b8) 56.48% compared to head (d6d8eb3) 56.04%.
Report is 7 commits behind head on main.

Files	Patch %	Lines
arbiter-core/src/middleware/mod.rs	0.00%	60 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #804      +/-   ##
==========================================
- Coverage   56.48%   56.04%   -0.45%     
==========================================
  Files          38       38              
  Lines        7637     7697      +60     
==========================================
  Hits         4314     4314              
- Misses       3323     3383      +60     

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[0xJepsen]

seems simple enough to me!