core/validatorapi: support proxy of SSE events

[DiogoSantoss]

The previous PR #4042 added eth2wrap logic (multi,lazy,etc) to proxied requests but broke SSE requests.
This PR fixes this issue by using proxy.ServeHTTP(proxyResponseWriter{w.(writeFlusher)}, clonedReq) to maintain a long lived HTTP connection between BN and VC.

category: bug
ticket: none

[codecov]

Codecov Report

❌ Patch coverage is 8.00000% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.36%. Comparing base (1cf3d3a) to head (6dcbc31).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
core/validatorapi/router.go	11.42%	30 Missing and 1 partial ⚠️
app/eth2wrap/lazy.go	0.00%	5 Missing ⚠️
app/eth2wrap/multi.go	0.00%	4 Missing ⚠️
core/validatorapi/validatorapi.go	0.00%	4 Missing ⚠️
app/eth2wrap/httpwrap.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4140      +/-   ##
==========================================
- Coverage   56.43%   56.36%   -0.08%     
==========================================
  Files         245      245              
  Lines       31175    31223      +48     
==========================================
+ Hits        17595    17598       +3     
- Misses      11272    11320      +48     
+ Partials     2308     2305       -3     

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[Copilot]

Pull request overview

This PR adds support for proxying Server-Sent Events (SSE) from beacon nodes by implementing a dedicated reverse proxy handler for the /eth/v1/events endpoint. The implementation extends the existing validator API infrastructure to handle streaming responses that require persistent connections.

Key changes:

• Added Address() and Headers() methods to client interfaces to support direct beacon node proxying
• Implemented eventsHandler using Go's httputil.ReverseProxy for SSE streaming
• Created proxyResponseWriter wrapper for error metrics instrumentation

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
core/validatorapi/router.go	Added SSE events handler with reverse proxy implementation and proxyResponseWriter wrapper
core/validatorapi/validatorapi.go	Implemented Address() and Headers() methods for Component
core/validatorapi/router_internal_test.go	Added Address() and Headers() methods to testHandler mock
core/validatorapi/mocks/handler.go	Generated mock implementations for new interface methods
app/eth2wrap/eth2wrap_gen.go	Added Address() and Headers() to Client interface definition
app/eth2wrap/httpwrap.go	Implemented Headers() method to return custom headers
app/eth2wrap/lazy.go	Added lazy wrapper implementation for Headers() method
app/eth2wrap/multi.go	Implemented Address() and Headers() methods for multi-client wrapper
app/eth2wrap/mocks/client.go	Generated mock implementation for Headers() method
testutil/beaconmock/beaconmock.go	Added Headers() method to Mock returning nil

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[pinebit]

Try using t.Context() wherever you can in tests.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud