Make delta writing more robust

[jrbourbeau]

Currently we're writing every table with write_delta

etl-github/preprocess.py

Lines 160 to 170 in 1b22e30

	def write_delta(tables: dict[str, pd.DataFrame]):
	for table, df in tables.items():
	outfile = OUTDIR / table
	outfile.fs.makedirs(outfile.parent, exist_ok=True)
	deltalake.write_deltalake(
	outfile,
	df,
	mode="append",
	storage_options=STORAGE_OPTIONS,
	partition_by="date",
	)

and using retries

etl-github/preprocess.py

Line 204 in 1b22e30

futures = client.map(write_delta, futures, retries=10)

which can lead to writing multiple copies of the same table. We should rewrite things so that can't happen.