Investigate switching sqlmesh core from freezegun to time-machine #3522
Description
The freezegun library allows you to "freeze time" in Python, which is valuable for reproducibility in unit tests.
SQLMesh users can specify an execution time (or other datetime variable) in their SQLMesh tests. Core implements this functionality using freezegun.
freeezegun has limited support for timezone handling, but the time-machine library has full support. We switched the sqlmesh unit test suite to time-machine in #3516 for this reason.
That PR did not switch sqlmesh core to time-machine, but we will want to at some point. The actual change is simple, the real task will be understanding the implications for DuckDB interoperability, etc.