[CT-2347] [Bug] Petite laideur in v1.5 logging: datetimes

[jtcohen6]

Since the switch to the new proto library, datetimes are ugly-rendered in text-formatted logging, and they take up more space than they should:

Timing info for seed.test.my_seed (execute): seconds: 1680366677
nanos: 785534000
 => seconds: 1680366680
nanos: 375668000

Command `dbt clone` succeeded at seconds: 1680366681
nanos: 79572000
 after 7.66 seconds

From looking at the JSON-formatted logs, this also shows up in the message field. Let's pretty-stringify these datetime values wherever they're being f-string formatted into message.

[jtcohen6]

Just ran into this one as well, during dbt deps:

14:45:21  [DepsNotifyUpdatesAvailable]: Unable to parse dict {'packages': ['dbt-labs/audit_helper', 'dbt-labs/dbt_external_tables', 'dbt-labs/metrics', 'entechlog/dbt_snow_mask', 'fivetran/hubspot', 'mjirv/dbt_datamocktool', 'fivetran/hubspot_source']}
14:45:21  Updates available for packages: []

Update: Already fixed by #7262!