refactor: Optimize the use of stellar_sdk.client.AiohttpClient.

[overcat]

When stellar_sdk.client.AiohttpClient cannot establish a Stream connection, stellar_sdk.exceptions.StreamClientError will be thrown.

[codecov]

Codecov Report

Merging #317 into dev will decrease coverage by 0.12%.
The diff coverage is 38.46%.

@@            Coverage Diff             @@
##              dev     #317      +/-   ##
==========================================
- Coverage   99.05%   98.93%   -0.13%     
==========================================
  Files         116      117       +1     
  Lines        5524     5611      +87     
==========================================
+ Hits         5472     5551      +79     
- Misses         52       60       +8     

Flag	Coverage Δ
#unittests	98.93% <38.46%> (-0.13%)	⬇️

Impacted Files	Coverage Δ
stellar_sdk/call_builder/base_call_builder.py	100.00% <ø> (ø)
stellar_sdk/client/aiohttp_client.py	85.34% <33.33%> (-2.33%)	⬇️
stellar_sdk/exceptions.py	90.32% <50.00%> (-2.79%)	⬇️
stellar_sdk/client/defines.py	100.00% <0.00%> (ø)
stellar_sdk/client/requests_client.py	98.29% <0.00%> (+3.29%)	⬆️