perf: reduce quest integration test runtime

[pratik50]

Summary

This PR reduces Quest integration-test runtime while preserving the existing test coverage.

Changes

• Consolidate the ingest/query smoke tests so they share one 120-second persistence wait.
• Consolidate the regular and custom-partition k6 smoke tests so they share one 150-second wait.
• Fix five load tests that previously false-passed because:
  • k6 VU/duration flags were malformed.
  • the same exec.Cmd was executed twice.
  • k6 failures did not fail the Go test.
  • the single-event script path was incorrect.
• Give every load test a unique stream.
• Register failure-safe stream cleanup using t.Cleanup.
• Remove the cross-test TestDeleteStream dependency.
• Ensure all five heavy load tests run only in load mode.
• Run the five isolated load tests concurrently using t.Parallel.
• Allow five parallel tests in the Quest container.

Runtime results

• Standalone: 24/24 tests passed in 16m58s
• Distributed: 24/24 tests passed in 16m53s

This reduces the time rage by approximately 11-12 minutes (~41%).