feat: add initial span tracing to http calls

[ldetmer]

This PR starts the implementation of low level HTTP tracing towards go/sdk:java-bigquery-observability.

It add an HTTP inteceptor to all HTTP requests and for now adds a few basic http request attributes to existing span. While we work through development all span changes will be gated through a system property: com.google.cloud.bigquery.http.tracing.dev.enabled which is disabled by default.

There is no change to existing telemetry (since flag is off).

example trace from this PR

Example trace before
change

[lqiu96]

Error:

2026-03-16T21:23:17.1945793Z 21:23:17:194 [ERROR] Tests run: 52, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.176 s <<< FAILURE! -- in com.google.cloud.bigquery.JobTest
2026-03-16T21:23:17.1947952Z 21:23:17:194 [ERROR] com.google.cloud.bigquery.spi.v2.HttpBigQueryRpcTest$TelemetryEnabled.testHttpTracingEnabledAddsAdditionalAttributes -- Time elapsed: 0.015 s <<< FAILURE!
2026-03-16T21:23:17.1949706Z org.opentest4j.AssertionFailedError: expected: not <null>
2026-03-16T21:23:17.1950878Z 	at org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:152)
2026-03-16T21:23:17.1952202Z 	at org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
2026-03-16T21:23:17.1953450Z 	at org.junit.jupiter.api.AssertNotNull.failNull(AssertNotNull.java:49)
2026-03-16T21:23:17.1954444Z 	at org.junit.jupiter.api.AssertNotNull.assertNotNull(AssertNotNull.java:35)
2026-03-16T21:23:17.1955784Z 	at org.junit.jupiter.api.AssertNotNull.assertNotNull(AssertNotNull.java:30)
2026-03-16T21:23:17.1957076Z 	at org.junit.jupiter.api.Assertions.assertNotNull(Assertions.java:304)
2026-03-16T21:23:17.1958602Z 	at com.google.cloud.bigquery.spi.v2.HttpBigQueryRpcTest$TelemetryEnabled.testHttpTracingEnabledAddsAdditionalAttributes(HttpBigQueryRpcTest.java:950)
2026-03-16T21:23:17.1960179Z 	at java.base/java.lang.reflect.Method.invoke(Method.java:569)
2026-03-16T21:23:17.1961266Z 	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
2026-03-16T21:23:17.1962301Z 	at java.base/java.util.concurrent.ForkJoinTask.awaitDone(ForkJoinTask.java:436)
2026-03-16T21:23:17.1963411Z 	at java.base/java.util.concurrent.ForkJoinTask.join(ForkJoinTask.java:670)
2026-03-16T21:23:17.1964361Z 	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
2026-03-16T21:23:17.1965588Z 	at java.base/java.util.concurrent.ForkJoinTask.awaitDone(ForkJoinTask.java:436)
2026-03-16T21:23:17.1966664Z 	at java.base/java.util.concurrent.ForkJoinTask.join(ForkJoinTask.java:670)
2026-03-16T21:23:17.1967879Z 	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
2026-03-16T21:23:17.1968811Z 	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
2026-03-16T21:23:17.1969959Z 	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
2026-03-16T21:23:17.1970887Z 	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
2026-03-16T21:23:17.1971891Z 	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)