temporal: Fix bare except statements with specific error handling

[arohanajit]

Fixes 5 instances of bare except (E722) in python/grass/temporal/:

core.py:

1. Line 55: ImportError is appropriate as it's specifically handling optional psycopg2 import
2. Line 417: Exception is used as get_tgis_metadata() is designed to return None for any metadata access failure
3. Line 1504: sqlite3.Error/psycopg2.Error catch database execution errors from their respective drivers
4. Line 1547: sqlite3.Error/psycopg2.Error catch transaction execution errors from their respective drivers

abstract_space_time_dataset.py:
5. Line 2466: FatalError/Exception handle mapset validation and database errors from interface layer

[echoix]

@arohanajit Can you address the conflicts when you have the chance?

[echoix]

Solved conflict in .flake8 file

[arohanajit]

@echoix Thanks for doing this, I got done with my finals just yesterday