[JS] Dates should be stored in TimestampMillisecond

[domoritz]

Describe the bug, including details regarding any error messages, version, and platform.

See duckdb/duckdb-wasm#1231

Component(s)

JavaScript

[amoeba]

Hi @domoritz, would you consider this change a breaking change under our definition?

[domoritz]

Yes-ish. The default behavior of how Dates are handled changes but I'd argue the previous behavior was wrong as it lost precision.