Fix buffer handling for large WebSocket messages

[brnbs]

The original code seems to have issues when proxying large messages. Increasing the buffer size using WithBufferSize() helps, but it also significantly increases memory usage. This PR uses a dynamic-sized buffer using a MemoyStream.

AspNetCore.Proxy.Tests running fine and also tested with large JSON messages manually.

[twitchax]

LGTM, but would you mind adding a test with a large message?

[codecov-commenter]

Codecov Report

Merging #88 (6e9cf28) into master (572fc3e) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 6e9cf28 differs from pull request most recent head 5d1ef86. Consider uploading reports for the commit 5d1ef86 to get more accurate results

@@            Coverage Diff            @@
##            master       #88   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines          660       669    +9     
=========================================
+ Hits           660       669    +9     

Impacted Files	Coverage Δ
src/Core/Extensions/Ws.cs	100.00% <100.00%> (ø)

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[brnbs]

Added a test, please check and create a new release when you have some time :)