Wire the SDK client to the application's HTTP client

[loevgaard]

Fixes #26

Stacked on #46.

Problem

The SDK Client was registered with only a setLogger() call, leaving the HTTP client, request factory and stream factory to php-http/discovery at runtime. That meant requests to Meta never appeared in the profiler's HttpClient panel, ignored any timeout, proxy, retry or scoped client configuration, could not be replaced by a MockHttpClient in tests, and depended on whichever PSR-18 implementation happened to be installed first.

Change

The Client definition now calls setHttpClient(), setRequestFactory() and setStreamFactory(), each with on-invalid="ignore". Symfony drops a method call whose argument cannot be resolved, so an application missing any of those services simply keeps the old discovery behaviour. Verified: in the test kernel psr18.http_client exists and the call survives, while the two PSR-17 factory services do not exist and those calls are removed.

New http_client option (default psr18.http_client) points the bundle at a different PSR-18 service, which is how you give Meta its own timeout. README.md shows the scoped client setup.

The client also joins the setono_meta_conversions_api Monolog channel.

Tests

• An end-to-end integration test replaces psr18.http_client with a Psr18Client wrapping a MockHttpClient, sends an event through the container's ClientInterface, and asserts the request was POST https://graph.facebook.com/v26.0/1234/events. That assertion only holds because the client is wired rather than discovered.
• A second test points http_client at a service that does not exist and asserts the container still boots.
• The mock is built by a factory (RecordingHttpClientFactory) because a container definition cannot hold a live object.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.00%. Comparing base (919b3dd) to head (2a07fca).

Additional details and impacted files

@@                       Coverage Diff                       @@
##             fix/25-log-dropped-events      #47      +/-   ##
===============================================================
+ Coverage                        76.70%   77.00%   +0.30%     
  Complexity                         139      139              
===============================================================
  Files                               30       30              
  Lines                              455      461       +6     
===============================================================
+ Hits                               349      355       +6     
  Misses                             106      106              

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