feat: add support for Soroban PRC's getTransactions and getFeeStats API interfaces.

[overcat]

#958

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.66%. Comparing base (bf27ba7) to head (465f2c9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #960      +/-   ##
==========================================
+ Coverage   98.64%   98.66%   +0.01%     
==========================================
  Files         253      253              
  Lines       13104    13213     +109     
==========================================
+ Hits        12927    13036     +109     
  Misses        177      177              

Flag	Coverage Δ
unittests	98.66% <100.00%> (+0.01%)	⬆️

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Files	Coverage Δ
stellar_sdk/soroban_rpc.py	100.00% <100.00%> (ø)
stellar_sdk/soroban_server.py	94.11% <100.00%> (+0.50%)	⬆️
stellar_sdk/soroban_server_async.py	97.05% <100.00%> (+0.25%)	⬆️
tests/test_soroban_server_async.py	100.00% <100.00%> (ø)
tests/test_soroban_server_sync.py	100.00% <100.00%> (ø)