fix: removing time machine to fix auth - #5975

this same root cause likely also affects tests/core/engine_adapter/integration/test_freshness.py. That file has 3 unguarded time_machine.travel(...) calls (lines 80, 208, 346) in tests that run against every engine via the shared ctx fixture — including bigquery, since make bigquery-test runs pytest -m "bigquery" and that marker gets applied to any test parametrized against the bigquery engine, not just this file.

Notably, test_freshness.py already has a precedent for this exact bug class — an autouse _skip_snowflake fixture with the comment "snowflake.connector generates an invalid JWT when time_travel changes the system time" — but nothing equivalent for bigquery. test_integration.py:2478 sidesteps it too, via if not ctx.is_remote:.

Since engine-tests-cloud only runs on main (not on PR branches), this won't show up in this PR's CI — but I'd expect those test_freshness.py tests to fail with the same invalid_grant error on the next post-merge cloud run. Worth either extending this fix to that file, or adding a _skip_bigquery-style guard, in this PR or a fast follow-up.

@mday-io -- so my defense is I wrote this test thats breaking stuff lol -- if I look at previous commits BigQuery started failing just on this test. I don't need time machine for it really though, just need a run to happen. I'll take a look at the snowflake fixture though, worth learning more about some of these tests. If some if these start randomly breaking we can investigate further, but I say good to merge