Refactor: starknet_estimateMessageFee

[hudem1]

rpc pkg cleanup according to #2437

Reuse v6 SimulationFlag and MsgFromL1 types for v7 and v8

As i was looking into refactoring starknet_estimateMessageFee endpoint, i just found those 2 types to refactor. I don't know if we really want to refactor those, but i opened a PR in case. Let me know if we don't necessarily want to refactor those

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 73.81%. Comparing base (482b6b5) to head (bcf7f71).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
rpc/v8/estimate_fee.go	33.33%	2 Missing ⚠️
rpc/v7/estimate_fee.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2496      +/-   ##
==========================================
+ Coverage   73.67%   73.81%   +0.14%     
==========================================
  Files         138      138              
  Lines       16918    16900      -18     
==========================================
+ Hits        12464    12475      +11     
+ Misses       3588     3560      -28     
+ Partials      866      865       -1     

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