feat(volo-http): add support for sse header validation

[Joshuahoky]

Motivation

Current implementation of sse has no validation of the Accept header on the server side

Solution

Added ResponseExt trait with is_sse() for checking if a response has Content-Type: text/event-stream
Added Accept header validation in Endpoint::call

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.15%. Comparing base (ff310f7) to head (632acea).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #645      +/-   ##
==========================================
+ Coverage   43.98%   44.15%   +0.17%     
==========================================
  Files         161      161              
  Lines       19750    19822      +72     
==========================================
+ Hits         8687     8753      +66     
- Misses      11063    11069       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.