Unit test for MeteredHttpClient (13 cases):
- duration emission with required OTel attributes
- response body size from Content-Length header
- request body size from explicit Content-Length header
- request body size from string body when no header
- no body metric when nothing measurable
- 4xx status code recorded without synthesized error.type
- transport failure (thrown exception) adds error.type
- excluded host skips emission entirely
- OTLP endpoint (OTEL_EXPORTER_OTLP_ENDPOINT) auto-excluded
- request() returns a MeteredResponse instance
- withOptions() returns a new instance preserving the decorator
- stream() unwraps MeteredResponse objects before delegating
- reset() clears the cached meter

BundleBootTest additions:
- http_client metrics disabled by default when metrics are enabled
- http_client metrics enabled sets container parameters for the pass
- validation rejects metrics.http_client.enabled without metrics.enabled

- Adds an HTTP Client table to the Metrics section listing the three
  instruments emitted, their stability status and attribute set.
- Updates the main config YAML block with metrics.http_client.enabled
  and metrics.http_client.excluded_hosts, mentioning the OTLP auto-
  exclusion.
- Notes that connection-pool metrics (http.client.open_connections,
  http.client.connection.duration, http.client.active_requests) are
  out of scope because Symfony HttpClient does not expose the pool.

Use FQCN per OTel semconv with a parent-class fallback for anonymous
classes, mirroring the messenger middleware fix.

…est.duration

The OTel SDK defaults are tuned for milliseconds and collapse all
sub-5s requests into the first bucket, making p95/p99 unusable.

Swallow exceptions from the body-size and duration histograms, and
move inFlight reset into a finally so a broken metric provider cannot
replace the original transport exception.

Replaces the inline anonymous-class fallback in MeteredHttpClient with
a reusable Util\ErrorTypeResolver, so the HTTP server subscriber and
the messenger middleware can share the same canonical implementation.

Adds MeteredResponseTest covering every public response method (header
finalisation with/without Content-Length, content/toArray success and
transport-failure paths, cancel, getInfo, getInnerResponse, double
finalisation idempotency, destructor fallback). Adds
HttpClientMetricsPassTest covering decoration of the default and tagged
HTTP clients, the disabled and missing-parameter early-returns, and the
empty-excluded-hosts fallback. Adds MeteredHttpClient cases for the
inFlight re-entrance short-circuit and reset() clearing the flag.

Without the SplObjectStorage map, chunks yielded by the inner client are
keyed on the bare response, so RetryableHttpClient (or any decorator
above this one) cannot look up the wrapper it handed in and Symfony's
AsyncResponse throws "UnexpectedValueException: Object not found".
Mirrors the fix applied to TraceableHttpClient in tracewayapp#35.