feat(volo-http): add sse client support

[Joshuahoky]

Motivation

SSE (Server-Sent Events) support was missing a client-side implementation for parsing SSE streams

Solution

Added SseReader for parsing SSE streams from server responses
Added SseExt extension trait on Response for converting a response into an SseReader via into_sse()
Added client and server examples demonstrating SSE usage

[codecov]

Codecov Report

❌ Patch coverage is 98.17073% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.87%. Comparing base (ff310f7) to head (7f13545).

Files with missing lines	Patch %	Lines
volo-http/src/client/sse.rs	98.17%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #644      +/-   ##
==========================================
+ Coverage   43.98%   44.87%   +0.88%     
==========================================
  Files         161      162       +1     
  Lines       19750    20078     +328     
==========================================
+ Hits         8687     9009     +322     
- Misses      11063    11069       +6     

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