bson roundtrip doesn't work with timestamp fields

[universalmind303]

Description

> create table timestamps (t timestamp);
Table created
> insert into timestamps values (arrow_cast(946684860000000, 'Timestamp(Microsecond, None)'));
Inserted 1 row
> select * from timestamps;
┌─────────────────────┐
│ t                   │
│ ──                  │
│ Timestamp<µs, UTC>  │
╞═════════════════════╡
│ 2000-01-01T00:01:00 │
└─────────────────────┘
> copy timestamps to  '/Users/me/Development/glaredb/out.bson';
Copy success
> select * from '/Users/me/Development/glaredb/out.bson';
Error: External error: Execution error: Unexpected datatype for builder Date64